3 point defense in the NBA: skill or luck?

Have you ever wondered about how much control a defense has over an opponent’s 3 point shooting?

On the one hand, there is obvious skill in closing out a shooter. This comes from proper positioning on the floor and alertness in identifying shooters.

On the other hand, jump shots from distance introduce randomness into the game of basketball. Every fan knows that feeling when their shooter gets hot and carries the team on a run. Then at other times, the shooter can’t throw the ball in the ocean. Live by the 3, die by the 3.

Analytics on 10 years of NBA data

I’ve been wondering about this for years, so I dug into NBA team data over the last 10 years. Two facts emerged.

First, there is randomness in team’s 3 point defense. Let’s measure 3 point defense by the percentage that opponents shoot from behind the arc. Then 3 point defense one season explains 2.7% of the variance in 3 point defense the next season, a correlation coefficient of 0.17. This percentage regresses strongly to the mean.

However, that’s not the entire story. Teams that play better defense within the arc tend to have better 3 point defense. Measured by field goal percentage, a team’s 2 point defense explains 20% of the variance in 3 point defense, a correlation coefficient of 0.45. Ken Pomeroy has found similar results for college basketball.

While there isn’t a strong correlation between 2 and 3 point defense, you can’t ignore that strong defensive teams, like Indiana last season, tend to allow lower 3 point field goal percentages. Indiana led the NBA in both 2 and 3 point field goal defense last season.

Preseason predictions for 2013

Analytics suggests that teams with poor 2 point defense but strong 3 point defense last year will not get so lucky again.

What if we used this idea before the 2012-2013 (last season as of this writing) to predict a team’s 3 point defense? In 2011-2012, New Orleans and Houston finished 2nd and 4th respectively in 3 point defense. However, both teams finished in the bottom 10 for 2 point defense. The next season, New Orleans and Houston ranked 27th and 22nd in 3 point field goal defense respectively.

What does that mean for the 2013-2014 season (which starts tonight)? Here are teams ranked by 3 point defense last season. Their rank in 2 point defense and field goal percentage are in parentheses.

1. Indiana 32.7% (1. 44.4%).
2. Memphis 33.8% (3. 46.5%).
3. Portland 34.0% (29. 51.2%).
4. Boston 34.2% (8. 47.2%).
5. Chicago 34.6% (5. 46.7%).
6. Oklahoma City 34.6% (2. 45.2%).
7. Golden State 34.7% (11. 47.3%).
8. Milwaukee 34.8% (14. 48.3%).
9. Philadelphia 34.9% (19. 48.7%).
10. Washington 34.9% (7. 47.0%).
11. Miami 35.0% (10. 47.3%).
12. San Antonio 35.3% (4. 46.6%).
13. Sacramento 35.5% (30. 51.2%).
14. Los Angeles Lakers 35.7% (15. 48.3%).
15. New York 35.7% (23. 49.8%).
16. Orlando 35.9% (25. 49.8%).
17. Dallas 35.9% (13. 47.5%).
18. Detroit 36.0% (22. 49.2%).
19. Toronto 36.1% (18. 48.7%).
20. Denver 36.3% (12. 47.4%).
21. Brooklyn 36.6% (20. 49.0%).
22. Houston 36.8% (16. 48.4%).
23. Minnesota 36.9% (24. 49.8%).
24. Utah 37.0% (17. 48.5%).
25. Cleveland 37.2% (28. 51.1%).
26. Los Angeles Clippers 37.3% (6. 46.8%).
27. New Orleans 37.4% (27. 50.5%).
28. Atlanta 37.9% (9. 47.3%).
29. Charlotte 38.8% (26. 50.2%).
30. Phoenix 38.8% (21. 49.2%).

Over at bettingexpert, I wrote about the implications of 3 point defense for Atlanta, the Los Angeles Clippers and Portland.

Video of Los Angeles Clippers and their “poor” defense

The Los Angeles Clippers are team that should have better luck in 3 point defense. However, this NBA.com video disagrees. It talks about how poor they defended the 3 point line, putting the blame on Carron Butler and Willie Green. Moreover, they show 6 examples of opponents making 3 point baskets.

Personally, I thought the Clippers closed out 2 of those shooters quite well. They gave up a third wide open 3 pointer off an offensive rebound. While the 3 other shots were poor defense, you can find three open 3 pointers against any team. Since the Clippers usually play good defense (6th in 2 point defense), expect the 3 point defense of the Clippers to rebound this season.

Thanks for reading.

Comments

  1. Is 3-point defense here defined only by opponent 3-point FG%? Since schedules are unequal in the NBA, shouldn’t the 3-point-shooting prowess of the opponents be factored in? Additionally, what about limiting 3-point shots altogether? The Spurs, a mediocre 3-point defensive team by FG%, focus a great deal of effort on eliminating 3-point looks by their opponents. I’d argue that the number of 3-point shots taken by an opponent in compared against their average number of attempts should factor in to a real 3-point defense metric.

    • Thanks for the thoughtful comment. No doubt, opponents should be factored into the analysis. Since I’m looking at season long data, there shouldn’t be too many differences in opponent’s shooting percent. But a more careful analysis would consider this.

      Your second point about not allowing 3 point shots is interesting. It depends on the opponent. I’d let the BObcats bomb away all night, but not let Steph Curry have any looks.

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