Can a defense in football force turnovers?

The 2011 Oklahoma State Cowboys were a turnover creating machine.

They forced 5 turnovers in 44-10 rout over Oklahoma in their Bedlam rivalry game that year. The turnovers had such an impact that Oklahoma didn’t score a touchdown until late in the 4th quarter despite racking up 358 yards. It gave Oklahoma State an astounding 42 turnovers created for the season, well above the 22 turnovers that an average bowl subdivision defense gets a year.

Moreover, the Cowboys preaches turnover creation in practice, as players are required to repeat plays or run afterwards if they do not force enough turnovers. In the two previous years, defensive coordinator Bill Young’s units had forced 34 and 30 turnovers, so Oklahoma State forced more turnovers than average for 3 straight years.

But can a team really force turnovers? Would the 42 turnovers in the regular season matter against Stanford in the Fiesta Bowl?

An analytic approach to turnovers

Bill Barnwell at Grantland has done the most complete study of forcing turnovers. After the Pittsburgh Steelers only forced 2 turnovers in their first 5 games of 2011, Barnwell asked whether turnovers in the first 5 games can predict turnovers in the remaining 11 games.

To answer this question, he looked at all NFL teams from 1990 through 2010 and calculated the correlation coefficient between early and late season turnovers. This coefficient is related to a scatter plot in which each point represents a team’s turnovers in the first 5 games on the horizontal axis and turnovers in the last 11 games on the vertical axis. The correlation coefficient describes the scatter of this plot. A value near 1 implies a high correlation. The points will all be near a line, meaning that lots of turnovers in the first 5 games implies lots of turnovers in the last 11 games. A coefficient near zero looks like a random scatter of points, implying no relation between early and late season turnovers. Wikipedia has pictures of what this looks like.

For his NFL study, which included over 600 data points, Barnwell found a correlation coefficient of 0.14, a very weak correlation between turnovers in the first 5 games and last 11 games. To think about this a different way, the square of the correlation coefficient is a measure of how much of the variation in the turnovers the last 11 games is explained by the turnovers in the first 5 games. Only 2% of this variation is predicted by early season results. Indeed, after getting only 2 turnovers in their first 5 games of 2011, Pittsburgh forced 12 turnovers in their last 10 games.

Barnwell’s study suggests that Oklahoma State’s high turnover total in the regular season is not useful in predicting future performance. So how did the Cowboys do in the Fiesta Bowl against Stanford?

Did Oklahoma State force turnovers against Stanford?

In the 1st quarter, Oklahoma State cornerback Justin Gilbert intercepted an Andrew Luck pass. It’s reasonable to argue that the Cowboys forced this turnover, as Gilbert had the speed and agility to step in front of the Stanford receiver.

In the 3rd quarter, Oklahoma State recovered a Stanford fumble. The replay clearly showed that Andrew Luck had a bad exchange with Geoff Meinken. In no way did Oklahoma State force this turnover. The defense capitalized on a mistake by the offense.

Stanford had 2 turnovers the entire game, nothing near the almost 4 turnovers per game the Oklahoma State defense had received during the regular season. It’s not that Oklahoma State didn’t try. On two catches in the 2nd half, Stanford receiver Griff Whalen had a horde of defenders standing him up and trying to rip the ball away. No luck.

Still, Oklahoma State won the game in overtime when Stanford missed a game winning field goal at the end of regulation.

Charles Tillman is the Picasso of forcing fumbles

Shortly after the Fiesta Bowl in January 2012, Chris Harry at SI.com wrote an article on the art of forcing fumbles. Defenders, such as Charles Tillman of the Chicago Bears, “have used running backs, wideouts and tight ends as their personal canvases to become Picassos when it comes to getting the football on the ground.” The article’s timing was impeccable after San Francisco’s Kyle Williams fumbled two punt returns in an overtime loss to the New York Giants in the NFC Championship game.

Harry clearly didn’t get the memo about Barnwell’s work. It gets even better when we dig into the numbers that support his argument for forcing fumbles. He states that Tillman forced a career high 6 fumbles in 2009. Since the Bears faced 1033 plays that season, he had a forced fumble rate of 0.6%. Not exactly Picasso.

It gets even better. Sports Reference claims that Tillman forced 6 turnovers in 2009, with 2 interceptions and 4 forced fumbles. It’s not clear whether Chicago recovered any of those fumbles.

Thanks for reading.