How computer rankings make you smarter about football

Predicting Super Bowl in 2016 was the ultimate test between eyes and numbers.

By the eye test, Carolina looked like the clear favorite over Denver. The Panthers had a stellar 17-1 record, and they destroyed two of the NFL’s best teams, Seattle and Arizona, to make the Super Bowl.

The eye test also favored Carolina at the quarterback position. Cam Newton had an Most Valuable Player caliber season, a touchdown machine at the pinnacle of his game.

However, the eye test for Super Bowl 50 didn’t hold up. In the first quarter, Von Miller stripped Cam Newton of the ball. Denver recovered for a touchdown that gave them a 10-0 lead.

Carolina’s offense never left the gate to take off for flight. Despite an anemic offense, Denver won 24-10 with the help of a few critical turnovers.

In contrast to the eye test, numbers suggested Denver wasn’t as overmatched as they seemed against Carolina in Super Bowl 50. This insight was based on computer rankings and their adjustments for strength of schedule.

Let me explain.

Margin of victory

It should be obvious that a team ranking system should consider margin of victory in games.

Do you care that Amazon has lower prices than your neighborhood book store? No. It’s the 40% discount on all titles that compels you to buy online.

The same lesson applies to computer rankings.

The Power Rank’s team rankings start with margin of victory in games. However, this raw metric didn’t tell the entire story about Carolina. The Panthers had an average margin of victory of almost 13 points, by far the best in the NFL in 2015.

Let’s take the next step.

Adjusting for strength of schedule

In a nutshell, computer ranking systems take a statistic like margin of victory and adjust for strength of schedule. That’s it.

This adjustment is more critical in college football than the NFL. In college, teams divide themselves into conferences of vastly differing strength. SEC teams play a much more difficult schedule than their neighbors in the Sun Belt.

In the NFL, the salary cap levels the playing field, which makes adjustments for strength of schedule less important than in college football. However, you shouldn’t ignore these adjustments, especially for Carolina during the 2015 season.

All of my team rankings take margin of victory in games and adjust for strength of schedule. Here are the NFL rankings prior to the Super Bowl with Carolina’s opponents in italics.

1. Carolina, 10.2
2. Seattle, 8.3
3. Cincinnati, 7.0
4. Arizona, 6.9
5. Kansas City, 6.8
6. Pittsburgh, 6.1
7. New England, 6.0
8. Denver, 5.2
9. Green Bay, 4.6
10. Minnesota, 3.7
11. New York Jets, 1.0
12. Buffalo, -0.4
13. St. Louis, -0.5
14. Oakland, -1.0
15. Detroit, -1.0
16. Houston, -1.0
17. Baltimore, -1.7
18. Philadelphia, -1.9
19. Chicago, -2.0
20. New York Giants, -2.2
21. Washington, -2.3
22. Atlanta, -3.1
23. New Orleans, -3.1
24. San Diego, -3.6
25. Indianapolis, -3.7
26. Dallas, -5.6
27. Tampa Bay, -5.8
28. Jacksonville, -5.9
29. San Francisco, -6.2
30. Miami, -6.4
31. Cleveland, -6.8
32. Tennessee, -8.9

Carolina played three teams in the top half of my team rankings the entire season. Their 6 division games against Atlanta (22nd), New Orleans (23rd) and Tampa Bay (27th) didn’t present much competition. In addition, they faced the weak teams from the NFC East and AFC South in other games.

Despite this strength of schedule, Carolina still ranked first in these points based NFL rankings because of their large unadjusted margin of victory in games. To find a potential weakness for Carolina against Denver, we need to dig further.

Rankings pass offense and defense

The Power Rank algorithm can do more than rank teams on adjusted margin of victory. It can also rank offenses and defenses based on efficiency metrics.

To get a better insight into the match up between Carolina and Denver, let’s look rankings for pass offense and defense. To do this, we take yards per pass attempt and adjust for strength of schedule.

This list gives the pass defense rankings before Super Bowl 50, again with Carolina’s opponents in italics.

1. Denver, 5.1
2. Carolina, 5.5
3. Seattle, 5.5
4. Kansas City, 5.6
5. Cincinnati, 5.6
6. Houston, 5.8
7. Green Bay, 5.9
8. New England, 6.0
9. Oakland, 6.0
10. St. Louis, 6.1
11. New York Jets, 6.1
12. Minnesota, 6.1
13. Pittsburgh, 6.2
14. Philadelphia, 6.2
15. Arizona, 6.3
16. Baltimore, 6.3
17. Buffalo, 6.6
18. Chicago, 6.6
19. Tampa Bay, 6.6
20. Indianapolis, 6.7
21. Detroit, 6.7
22. Dallas, 6.7
23. Washington, 6.8
24. Atlanta, 6.8
25. Tennessee, 6.9
26. Jacksonville, 6.9
27. San Francisco, 7.0
28. San Diego, 7.0
29. Miami, 7.1
30. New York Giants, 7.2
31. Cleveland, 7.3
32. New Orleans, 7.9

Cam Newton only faced three solid pass defenses all season. Three!

I should note that Arizona’s pass defense would have made a fourth good pass defense before Carolina racked up 11.2 yards per attempt against them in the NFC championship game.

Carolina threw for almost 7 yards per attempt, 5th best in the NFL. However, strength of schedule adjustments drop Carolina to 11th in the pass offense rankings.

Also, Denver had the top ranked pass defense heading into the Super Bowl. The number next to each team gives a rating, or expected yards per pass attempt allowed against an average pass offense. Denver had a rating significantly better than second ranked Carolina.

Numbers over the eye test

It wasn’t easy trusting the numbers before Super Bowl 50. Everyone liked Carolina, as the markets closed with the Panthers as a 5 point favorite over the Broncos.

My member predictions, which use a number of metrics including the rankings discussed in this article, gave Carolina a 1 point edge. While this seemed a bit low, the match up of Denver’s pass defense against Cam Newton gave the Broncos hope.

In the game, Newton threw for 4.1 yards per pass attempt, well below his season average. This played a big role in Carolina’s loss to Denver, as numbers and analytics stood strong against the eye test in this game.

Manning versus Newton: Previewing the Super Bowl, 2016

sb_trophyWill the Broncos or Panthers win Super Bowl 50?

As usual in professional football, this question will get answered by the quarterbacks, Peyton Manning and Cam Newton. Put bluntly, it’s the old man versus one of the most athletic human beings in the world. If you didn’t follow sports, you would never guess which one of these guys is being investigated for PED use.

However, both teams have excellent defenses as well. How do they match up against Manning and Newton? Let’s break it down.

Panthers offense versus Broncos defense

The real matchup in this game is the Broncos’ defense against Cam Newton. I would say the Panthers’ offense, but he’s the only above average skill-position player.

As noted in my conference title game preview, the Broncos have the top ranked defense by yards per pass attempt and sack rate, both adjusted for schedule. (They’re slacking against the run, ranking only 2nd best in the NFL.) However, Cam Newton presents an entirely new problem.

Not only is Newton bigger than most linebackers, he’s one of the fastest quarterbacks in the NFL. I have little doubt that Von Miller, DeMarcus Ware, and others can flush Newton from the pocket. However, can they then tackle him?

I thought the Cardinals had their chances to tackle Newton in the NFC championship game but were not able to bring him down (or tackle any one else on the Panthers offense).

I don’t foresee the Panthers’ wide receivers beating the best pass defense in the NFL on initial routes. However, they could make plays if Newton has or creates time to throw. Covering wide receivers may be the hardest job in the NFL. The longer corners are required to cover, the harder it becomes.

The Broncos must contain Newton and make him throw into coverage earlier than he would like.

Broncos offense versus Panthers defense

On the other side of the ball, the Panthers’ defense will not have the same worries. Peyton Manning is as immobile as they come and his arm strength has diminished.

To my surprise, the Broncos came out throwing the ball more than expected last week. Manning protected the ball well, took his sacks when pressured, and did just enough to win the game.

Though I’m still not a huge believer in the Panthers’ secondary, the front seven is solid. They will be able to sit on under routes and short crosses that Manning prefers these days.

Prediction

Despite the Broncos’ shortcomings on offense, there is still value on their side in this game. Pinnacle opened with the Broncos as a 3.5 point underdog, but that number has moved as high as 6. It has settled at 5.5 on Tuesday before the game, while The Power Rank’s member numbers makes the Broncos a 1.1 point underdog.

The difference between the computer projection and the markets is the current state of the Broncos. They’re not as strong as earlier in the season. The recent play is determining the point spread more than season-long statistics.

The question becomes whether or not we should trust recency bias or season-long statistics. I’d prefer to look at the season as a whole, but I can see the case for expecting a blowout in favor of the Panthers.

Personally, I lined this game closer to the open (Broncos +4) and am willing to play it at the current number. With both defenses being very stout, I am expecting a closer game than the Panthers’ have seen lately. It would not surprise me to see the line get bumped back down towards +5 or +4.5 at sharper books. Not to mention, backing the opposite of the public favorites in the NFL has proven to be profitable.

Coming back from behind will prove difficult for the pedestrian Broncos’ offense. They will need to get ahead or keep the game close in the first half to have a chance in Super Bowl 50.

I’m willing to entertain both narratives of this game. Seeing Newton growing into a superstar with relatively no help on offense has been incredible. Manning likely has one foot out of the door, and I wouldn’t mind seeing the old man go out with a ring.

Unfortunately, if Manning does get his ring, it will be a similar story as the AFC championship game. We will credit Wade Phillips’ NFL best defense and incredible game plan to contain Newton. Otherwise, it’ll be another disappointing playoff scenario for Peyton and the near perfect season for the Panthers.

Preview of the NFL conference championships, 2016

sb_trophyWhich teams will make the Super Bowl?

New England travels to Denver as a 3 point favorite. This goes against the numbers, but a strong subjective adjustment suggests that the markets have this one correct.

The story is different for Arizona at Carolina. A look at the match ups and injury situations go against the home favorite Panthers in the NFC championship game.

Let’s take a closer look at both games using the ensemble predictions available to members of The Power Rank.

Patriots at Broncos (Line: +3, The Power Rank: -3.8)

Both the Patriots and the Broncos have played two different seasons. Both teams started the season on fire, then struggled down the stretch.

Though their win-loss record didn’t take a big hit, the Broncos didn’t quite fit the part as the number one seed in the AFC. They’ve been flip-flopping between an “injured” Peyton Manning and the youngster, Brock Osweiler.

The defense kept the Broncos a consistent force all season. Despite, to be fair, awful play at quarterback by both Manning and Osweiler, the Broncos won important games down the stretch on their way to the number one seed.

What made the number one seed possible for the Broncos? The Patriots’ struggles.

After starting 10-0, the Patriots finished the season 2-4 as injuries affected the offense and the secondary struggled.

In my opinion, the Patriots didn’t exactly try to win the last two games of the season. They kicked off in overtime against the Jets and only threw the ball a handful of times against the Dolphins.

I would agree that avoiding the Steelers as the sixth seed was a better opportunity for the Patriots to reach the Super Bowl. With the Broncos knocking off the hobbled Steelers last weekend, this week is an even better opportunity for the Patriots.

The Patriots offense is suddenly healthy. With Danny Amendola, Julian Edelman, and Rob Gronkowski all appearing close to 100% last week, Tom Brady ripped apart the Chiefs’ solid defense and silenced many doubters (including me).

The discrepancy in The Power Rank’s prediction (Broncos by 3.8) and the actual point spread (Patriots by 3) likely comes from the way these teams are trending health-wise. The Patriots statistical struggles down the stretch could be credited to both not exactly attempting to win games and preserving health for this very moment.

This current Patriots team is much closer to the team that started 10-0 as opposed to the team that closed the season 2-4 while losing to Brock Osweiler in overtime.

Though the Broncos’ defense is extremely stout (the best pass defense and sack rate in The Power Rank’s ratings), quarterback play will hold back this team. They rank just 19th in pass offense and yards per carry (both adjusted for strength of schedule).

I have sympathy for those currently backing the Broncos this week. There is some line value on a team with a great defense getting 3 points at home. But the uncertainty at quarterback position is frightening.

If you are a follower of The Power Rank, you know that rushing ability does not predict wins or losses. The Broncos must be willing to throw the ball on the Patriots’ secondary if they want to stay in this game.

Seeing that they were not willing to throw the ball against the Steelers awful secondary last week, I would not back either team of these teams. Point spreads are pretty efficient this time of the year and I don’t see the number coming off of three on either side throughout the week.

At 3 points, I’ll pass on the side and enjoy the last of the Brady-Manning rivalry that we’ve been blessed with for so many years.

Cardinals at Panthers (Line: -3, The Power Rank: +0.2)

A Cardinals-Panthers matchup is the most we could ask for this NFL season. These teams are very similar on paper and the point spread would suggest they are equals on a neutral field.

Both of these offenses are extremely talented, exciting, and efficient. Both defenses rank in the top twelve in the passing game. Lastly, the most underrated portion of this game is the aggressiveness of coaches Bruce Arians and Ron Rivera.

Though they have beat them twice, the Seahawks are by far the best team the Panthers have played this season. Their own division was very weak and their schedule-matched division this year was the NFC East. That combination alone led to an opponent 47-65 record.

The Panthers did beat the Packers, but we can all admit it wasn’t the typically strong Green Bay team. Overall, Carolina only played two teams in the top half of The Power Rank’s member rankings: Seattle and Green Bay.

The Power Rank’s advantage for the Cardinals comes from pass offense, 1st in the NFL, against the Panthers pass defense. After accounting for strength of schedule, the Panthers pass defense is merely average, 16th in the NFL.

I would agree with this assessment. Outside of Josh Norman, the Panthers secondary is questionable at best. Robert McClain, Cortland Finnegan, and Roman Harper are all liabilities when trying to cover Larry Fitzgerald, John Brown, and Michael Floyd. Admittedly, Kurt Coleman has had a huge year with seven interceptions; however, this appears to be more of an aberration when you consider his previous seasons.

Let’s not downplay Cam Newton’s talent, either. He’s lost a total of one game this season while scoring loads of points despite being the only offensive threat on the team. You’ll have to forgive me as this is also my concern.

When looking at the matchup for the Cardinals secondary against Ted Ginn, Devin Funchess, and Kevin Norwood, I can’t say Cam has the upper hand this week.

Playing at home certainly does help. But if you’re giving me the entire three points with a good quarterback, the better secondary, and much better receivers, I’m going to take that every time. I may not agree that the Panthers should be underdogs in this game at home, but the whole three points is too many.

You can follow Frank Brank on Twitter.

Predictions for the NFL Divisional Round Playoffs, 2015

2014_DivisionWhat’s the NFL without a little controversy? All news is good news for the NFL. The more folks blowing up social media on the missed pass interference call in the Cowboys-Lions game only made more tune into the game.

Conspiracy theorists rejoice.

Overall, I had a pretty solid Wildcard Round last week. Many of the outcomes ended up being as predictable as I had thought. This week will be a little more difficult as the teams get better, the weather gets worse, and the lines get tighter.

Ravens @ Patriots

The first game of the week renews the heated Flacco-Brady rivalry… just kidding.

The Joe Flacco in the Playoffs narrative continues after the Ravens beat the Steelers in Pittsburgh last week. Though his team’s record is impressive in recent years, let’s not depend on a small sample of games spread out across multiple seasons. Flacco will undoubtedly regress towards his career expectancy.

Flacco hasn’t played well on the road in his career. In 56 home games, Flacco has completed 61.7% of his 1740 passes for 7.56 yards per attempt (78 touchdowns, 35 interceptions). In 56 road games, he drops to 59.5% completion rate on 1907 attempts for 6.45 yards per attempt (70 touchdowns, 55 interceptions).

Those road numbers compare to teams like the 49ers, Titans, and Jaguars from this year. For what it’s worth, I quickly scrolled through home/road splits of other quarterbacks like Tony Romo, Peyton Manning, Tom Brady, Ben Roethlisberger and even Andy Dalton without finding a home/road difference even close to Flacco’s.

In addition, he will face New England’s 11th ranked pass defense and 12th best sack rate. That’s quite the step up from Pittsburgh’s abysmal secondary and pass rush.

The Patriots offense, ranked 6th by The Power Rank, also has a favorable match up. Tom Brady will draw the Ravens league average pass defense (15th).

Baltimore does make up for the secondary by getting after the quarterback. The Power Rank predicts they sack the opposing quarterback on 8.25% of pass attempts against average pass protection. The issue, of course, is Tom Brady doesn’t take many sacks. New England gives up a 3.7% sack rate against an average pass rush, second best in the NFL.

If you’re backing the Ravens because of Joe Flacco’s recent playoff success, you should look at the difference in his home and road performance. He doesn’t play well on the road compared to other quarterbacks.

Markets opened this game at Patriots -8.5. With some money coming in early, this line was adjusted moved down to Patriots -7.

This game is appropriately lined given the Patriots home dominance over the last decade; however, there’s some clear line value any time you can get an underdog north of seven points. Baltimore is still getting the slim majority of the bets, so this line has a small chance to get under seven points. The value would then be flipped to the Patriots.

I’ll take the Patriots to win with comfort and hope the Joe Flacco in the Playoffs story is put to rest.

Panthers @ Seahawks

The Panthers and Seahawks couldn’t be further away in the standings. However, they play similar styles of football with an aggressive defense and run first offense.

Throughout the season, the Seahawks executed that style better since they had 12-4 regular season record versus the 7-8-1 mark of the Panthers.

Continuing with the similarities, each of these teams have played some cupcake games recently. Seattle finished the season winning six straight games with two games against quarterback-depleted Arizona, two against San Francisco, Philadelphia, and St. Louis.

Carolina has won five straight against New Orleans, Tampa Bay, Cleveland, Atlanta, and a quarterback-depleted Arizona. Nonetheless, these are still professional football players and no opponent should be taken for granted.

The Panthers and Seahawks each have elite defenses. The Panthers defensive numbers are a little skewed as they’ve gotten healthy as the season has progressed and have played much better as of late.

According to The Power Rank, they still rank 13th on defense with the seventh best pass rush. Sacks have disrupted Russell Wilson and the Seahawks offense all season (8.8% sack rate).

I don’t believe this is a knock to the offensive line; Wilson has held onto the ball entirely too long. Lacking a real threat on offense could be the issue.

The Seahawks traded away Percy Harvin, leaving Doug Baldwin and Luke Wilson as the most dangerous weapons on offense. Wilson has been able to improvise with his legs; however, there is no doubt in my mind that Luke Keuchly will be spying him all game.

The Seahawks offense, ranked 17th, should struggle against a fast, opportunistic Carolina defense.

The Panthers offense will be in a similar situation. The Seahawks, who also struggled on defense at the start of the season by their standards, have worked their way up to the fifth best defense per The Power Rank.

Cam Newton has played better lately, but I expect him to have similar issues as Russell Wilson in this game.  Newton certainly has more weapons at his disposal, but he’ll also oppose the better defense.

The books have lined this game at Seahawks -10.5 after opening at Seahawks -11. This game should be much closer than that. Even with the Panthers playing much better lately, 56% of the public has laid all those points with the Seahawks.

I simply don’t think the Seahawks can score enough points to cover a double digit line. I’m going to go out on a limb and say the Panthers have a good chance to win this game with such limited scoring. One big play can change the outcome.

Cowboys @ Packers

The Cowboys narrowly scraped by last week, as we thought they might, with a little help from the referees, of course. The Packers had a week to rest, which should only help them continue their home dominance.

The Packers have a ridiculous offense, which you don’t need me to break it down. The Cowboys also have a great offense, so where is the edge for each team?

For starters, the Cowboys defense is not very good. I was supremely impressed by their second half against Detroit. They shut down the running game, pressured Stafford, and held the Lions offense to three points.

However, the Cowboys defense was terrible in the first half against Detroit. If they lay an egg in either half of this game, Aaron Rodgers will take advantage and put them away early considering the Cowboys defense ranks 27th in passing defense and 29th in sack rate.

The Packers defense may have similar issues. Though the offense started slow last week, the Cowboys have roughed up even the best of defenses, including the Seahawks in Seattle.

According to The Power Rank, Green Bay’s defense now sits 24th in passing defense and 17th in sack rate. They have certainly been better than Dallas, but it’s not a wide margin by any means.

Even with temperatures expected to be around twenty degrees at game time, I expect some points. The books expect the same with a total of 53, only trailing the Broncos-Colts total by one point.

Having an opinion on this game is difficult. I really do trust Green Bay’s home dominance, but I also trust that they will give up some points.

There’s certainly a chance the Cowboys hang in there and win this game, but I wouldn’t bet on it.

The Power Rank has the Packers by a touchdown and I agree with that number. The betting line is also hovering around Packers -6.5.

On a neutral field, these teams are very close to equals. At Lambeau, I’ll take the Packers over any team.

This is a rare game where the hot and cold of the Cowboys isn’t swaying their betting line. If you’re going to take a side, grab the Cowboys and the points, but the books got this one right.

Colts @ Broncos

Many thought the Colts were in trouble after the closing weeks of the regular season. However, their offensive line dominated the Bengals pass rush in their Wildcard game and gave Andrew Luck plenty of time to find his speedy receivers.

The Broncos got the week off they desperately needed. They have some injuries on their offensive line.  Even the Bengals horrendous pass rush was able to exploit those soft spots up front.

The Broncos face a good Colts pass rush ranked 9th in sack rate adjusted for schedule. They also have a good secondary, as the Colts pass defense is very underrated at 10th in The Power Rank.

The Broncos front will be better this week than in recent weeks. Though it’s a tall task with his quick releases, but if the Colts front seven can disrupt Peyton, they might have a chance to win this game.

Ed and I have talked previously and agree that the Broncos are a better team, at least statistics-wise, than they were last year at this point.

The Broncos are the top ranked team in The Power Rank and have the second best pass defense with a strength of schedule adjustment for yards per attempt.

Peyton Manning still has the best overall protection with the aid of his quick timing routes and the best passing attack. Very few would question that.

The questionable part is their now run-happy offense. C.J. Anderson has emerged as one of the better power backs with added quickness in the league. Realistically, though, Peyton Manning should be throwing the ball more often, as he leads the top ranked pass offense.

If the Colts want to survive and advance, they’ll need to get to Manning. It’s that simple. If he has time in the pocket, Manning has proven for nearly two decades that opposing teams have a very small chance to beat him.

I don’t foresee the pressure being sufficient and expect the Broncos to win comfortably. The books have lined this around a touchdown. The Power Rank likes the Broncos by a little more with an ensemble prediction of -8.6.

The difference is the key number of seven points. You want to be on the correct side of that number. I can live with laying 6.5 points with Denver. You probably won’t see less than a touchdown anywhere, though. I also wouldn’t be opposed to taking the points at Colts +7.5.

Outlook

I really can imagine two of the underdogs, Panthers and Cowboys, winning this week. I would rank them in that order of likelihood, as well. The Panthers being double digit dogs may disagree with me, but I love the match up.

With no games inside of 6.5 points in Vegas, they are suggesting a pretty boring Divisional round. However, we know well enough the playoffs are always exciting. Sports have insanely random outcomes in the one game samples you’ll get this week.

Frank Brank founded cheapseatanalytics.com, a site devoted to analytical sports information and betting systems. He majors in baseball but also covers the NFL and NHL. You can follow him on Twitter @realFrankBrank.

How to predict interceptions in the NFL, backed by surprising science

photoTurnovers play a critical role in football.

A tipped pass for an interception or crushing hit for a fumble can decide a close game. No coach emerges from a press conference without touting the importance of winning the turnover battle.

However, not all turnovers are created equal. In the 2013 NFL regular season, teams with more interceptions than their opponent won the game 80% of the time. Teams that forced and recovered more fumbles than their opponents won the game 70% of the time.

Interceptions have a bigger impact because the defender is most likely on his feet after the takeaway. This can lead to a big swing in field position or even a score. Defenders that recover fumbles tend to fall on the ball.

What factors affect interceptions in the NFL? Here, we’ll look at the surprising analytics behind interceptions.

You can do better than guessing that each team will throw picks on 2.9% of pass attempts, the NFL average. And it doesn’t involve an arcane statistic that comes from charting games. The critical numbers are in the box score, although it might not be the numbers you expect.

We’ll also look at how this analysis changes the predicted point spread for a game.

How pass rush affects interceptions

Seattle cornerback Richard Sherman led the NFL in interceptions in 2013. Despite all of his public claims about being the best cornerback in the league, Sherman credits his front seven for much of his success.

Pass rush is an obvious candidate to affect interceptions. The more often a defense applies pressure on the quarterback, the more often he throws an errant pass. Or perhaps the defender strikes the quarterback’s arm, causing a wobbly pass to fall into the hands of the defense.

To study this, we need to measure the strength of the pass rush. To start, let’s look at sacks, a number that requires proper context. A defense might rack up more sacks by facing more pass attempts. To account for this, let’s use sack rate, or sacks divided by the sum of pass attempts and sacks, as a measure of pass rush.

To determine whether pass rush causes interceptions, consider NFL defenses in the regular season from 2003 through 2013. While I expected defenses with a better sack rate to have a higher interception rate, there’s no correlation between these two quantities for these 352 defenses.

For those with a technical inclination, sack rate explains less than 1% of the variance in interception rate. For everyone else, check out the left panel of the visual in the next section.

Richard Sherman might be a great cornerback because of Seattle’s pass rush. However, his pass rush doesn’t explain his high interception total in 2013.

How pass protection affects interceptions

If pass rush has no effect on a defense’s interceptions, what about pass protection on offense? An offensive line that keeps pass rushers away from the quarterback might result in fewer interceptions.

Over the same 11 regular seasons, the sack rate allowed by an offense explains 6% of the variance in the interception rate. While this correlation is stronger than on defense, I still do not recommend using sacks to predict interceptions. The right panel of the visual shows why.

nfl_sack_pick_corr

We can dig even deeper into pass protection. Over the last 5 seasons, the NFL has tracked QB hits, or the number of times the quarterback gets hit after releasing the ball. We can now calculate the rate at which an offensive line allows the hits on the quarterback (the sum of QB hits and sacks divided by the sum of pass attempts and sacks).

This QB hit rate gives a better perspective on pass protection. An offensive line might look good because of a low sack rate. For example, Indianapolis gave up sacks on 5.2% of pass attempts in 2013, 5th best in the NFL.

However, this same offensive line allowed a hit rate of 23%, 26th worst in the NFL. Andrew Luck’s ability to get rid of the ball in the face of pressure played a big role in their low sack rate. The lack of protection probably also contributed to Luck’s below average completion percentage of 60% in 2013.

However, even a better statistic like QB hit rate doesn’t correlate with interceptions. Hit rate explains 4% of the variance in interception rate, a weaker correlation than shown in the right panel of the visual.

The data does not support the belief that pass rush affects interceptions. I would guess this comes from the ability of NFL quarterbacks to not let pressure to affect their accuracy. Of the thousands that play in high school and hundreds that make it to college, only 32 can play in the pros. These quarterbacks do not fold under pressure.

However, these 32 quarterback do vary in their accuracy, and that might impact interceptions.

How throwing accuracy affects interceptions

Despite the wobbles of the his balls, Peyton Manning has shown incredible precision with his throws. Over his career, he has completed 65.5% of his passes. Of active players, only Drew Brees and Aaron Rodgers have a better career completion percentage.

However, Peyton has gotten even better after having multiple neck surgeries. In his last two seasons with Denver, his completion percentage has increased to 68.4%.

Do more accurate quarterbacks throw fewer interceptions? Any fan would rather have Manning and Rodgers leading their offense than Derek Anderson or Brady Quinn. But are fewer interceptions a consequence of a better quarterback?

To answer this question, consider the career statistics for NFL quarterbacks in 2013 with at least 500 career pass attempts. The visual of these 52 players shows the negative correlation between completion percentage and interception rate.

nfl_qb

Peyton Manning is the third point from the right, and he has thrown picks at a higher rate than this regression analysis predicts. Aaron Rodgers has the lowest interception rate of the 3 quarterbacks with better than 65% completion rate.

The outlier with the lowest interception rate is Nick Foles, the second year quarterback with Philadelphia. As much potential as he has shown, he will not continue to throw interceptions on 1.2% of his pass attempts. The same applies to San Francisco’s Colin Kaepernick, the point with the second lowest interception rate (1.7%).

This correlation does not imply that better accuracy causes fewer interceptions. But this conclusion does seem logical. The quarterback has control over where he throws the ball. The more control he shows, the less likely the ball hits the hands of a defender. There are better ways to look at this causation, but they will have to wait for another day.

For these quarterbacks, completion percentage explains 32% of the variance in interception rate. In the noisy world of football statistics, that’s as strong a relationship as you will see between two statistics. In addition, the correlation also exists for the regular season statistics of offenses from 2003 through 2013. Here, completion percentage explains 20% of the variance in interception rate.

With this strong relationship between accuracy and interceptions, how can we modify a point spread prediction for a game?

How interceptions affect the point spread

To use these results to adjust a prediction, let’s look back at the Super Bowl between Seattle and Denver at the end of the 2013 season. Before the game, the team rankings at The Power Rank predicted Seattle by 1.3 points, which implied a 46% chance for Denver to win.

Denver had a lower likelihood to throw a pick based on Peyton Manning’s accuracy. On average, NFL quarterbacks throw interceptions on 2.9% of pass attempts. With Peyton’s 65.5% career completion percentage, the regression model predicted he would throw interceptions on 2.56% of pass attempts. For a league average 35 pass attempts, this meant 0.14 fewer interceptions for the game.

While such a small fraction of picks might seem inconsequential, the impact of such a turnover makes it matter. From the relationship between interceptions and points in NFL games, the average interception is worth about 5 points. This changed the predicted point spread by 0.7 points in Denver’s favor. Seattle’s predicted margin of victory dropped from 1.3 to 0.6, which increased Denver’s win probably from 46% to 48%.

The game didn’t go Denver’s way. Seattle’s defenders knew what mouthwash Manning used before the game since they spent the entire game in the backfield.

The outcome of interceptions in the Super Bowl

Manning thew 2 interceptions. The first was an errant pass that landed in the hands of Cam Chancellor, a play in which Manning wasn’t pressured that heavily. The second pick came when a defender hit his arm on a throw. The football wobbled into the hands of Malcolm Smith, who ran for a Seattle touchdown.

For the game, Manning thew 49 passes, so the two picks implied a 4.1% interception rate. Even with this small sample size, that is not an outrageous rate. If not for the bad luck on the pick in which his arm got hit, Manning would have had a 2% rate.

Common sense says that pass rush and throwing accuracy affect interceptions. However, the NFL data only shows a link with one of these factors. If you want to predict interceptions, stay away from pass rush statistics and look at completion percentage.