3PT defense

[kso_FAN]

Good article from kenpom about an interesting defense trend. (at least it was to me)

Surprised 3PT attempt percentage defense correlates so high, especially that it correlates higher than 2PT percentage defense.

It's no secret that a big factor in the Wisconsin Badgers' success this season has been their defense. The Badgers' offense has averaged a pedestrian 1.02 points per possession in Big Ten play -- ninth-best in the conference -- but Wisconsin has the third-best efficiency margin thanks to a defense that has limited Big Ten foes to 0.95 points per trip.

Wisconsin's offense is not potent enough to pull away from quality competition, but its defense has been good enough to keep the team in almost every game this season. Just four times has a Badgers opponent topped a point per possession, and no team has done better than the 1.08 PPP that Michigan scored on the Badgers on Jan. 8. Say what you want about Wisconsin's style, but its defense has been very effective even when you take into account that the Badgers play at the nation's slowest tempo.

A sizable component of their defensive success has come on the perimeter. Wisconsin has held opponents to 26.2 percent accuracy from beyond the arc, which is second-best nationally, and there is no doubt that has contributed to the overall statistical success of the defense. But the Badgers' defense is built for continued success not because of its 3-point percentage defense, but because the Badgers limit their opponents' 3-point attempts. This is because Wisconsin, or any other college basketball team, has surprisingly little control over their opponents' accuracy from long distance.

One way to get an idea of a team's influence on a particular statistic is to look at how well it correlates from season to season. The correlation between a team's defensive 3-point percentage from 2010 to 2011 was .204. That number is meaningless on its own, so allow me a few sentences to provide some context.

First, for the non-math majors, correlation is a value between zero and one where, in this case, zero would indicate there is no relationship in opponents' 3-point percentage from season to season, while a value of one would indicate perfect predictive powers. If the correlation in our case was a one, a team that led the nation in 3-point defense one season would lead it the following season. In order to provide context for what a correlation of .204 means in basketball terms, let's compare that figure to the season-to-season correlation of other team stats:

Opponents' 3-point percentage: .204
Opponents' free throw percentage: .266
Opponents' 2-point percentage: .558
Opponents' 3-point attempt percentage: .575

There are just four numbers here, but they provide a very powerful context. What stands out is that opponents' free throw percentage correlates more strongly from season to season than opponents' 3-point percentage. In other words, we can predict a team's "free throw defense" in the future based on current stats better than we could predict its 3-point defense. And I think everyone understands that a team has little control over its opponents' free throw percentage.

Virginia's opponents are shooting 61.5 percent from the line -- second-worst in the country -- but I have yet to see an analyst tout the Cavaliers' free throw defense because such a thing doesn't exist. The reason there's any correlation at all is because a team's schedule is made up of similar opponents from year to year and those opponents have similar players, so naturally there is some relationship in opponents' free throw percentage from season to season, but it's very small.

However, the same mechanics are at work for 3-point shooting and yet there's even less of a relationship in a team's defensive 3-point percentage from season to season. Many folks will evaluate a team's perimeter defense based on the 3-point percentage a team allows, but this evidence suggests that we need to seriously rethink that approach. A team has some control over how well its opponents shoot, but it's significantly less than many might believe.

Notice that opponents' 3-point attempt percentage is much more stable from season to season, which is a major clue that a team has more control over its opponents' 3-point attempts than their 3-point accuracy. Both Duke and Saint Mary's have been consistently spectacular at preventing attempts during the past decade -- only once during that time has either team finished outside the top 10 in defensive 3-point attempt percentage. You won't find teams that have had anything close to that kind of run in 3-point percentage because of the effect just described.

It's pretty clear that Wisconsin's defense isn't a fluke and that its ability to make it difficult for opponents to score will continue. But its 3-point percentage defense is not high on the list of reasons for that. The Badgers' defense should be feared because it is good at the things a defense has the most control over -- opponents' 2-point percentage and opponents' 3-point attempts.

Wisconsin has held opposing teams to 39.7 percent inside the arc this season, ranking fourth in the country. In addition, the Badgers limit 3-point attempts about as well as anyone. Badgers opponents have taken just 23.3 percent of their shots from 3-point range, which is second in the nation. Ohio State took just seven 3-pointers against Wisconsin last Saturday, and it would be surprising if Minnesota cracks double-digits in that department Thursday. When opponents take but a few shots from long range, a team isn't going to be affected much by hot 3-point shooting.

A great example of the opposite extreme was provided in Wednesday's classic between North Carolina and Duke. The Tar Heels play stellar interior defense and lead the ACC in 2-point percentage allowed, but they're dead last in 3-point attempt percentage. Duke got hot from long range, and when you give up 36 3-point attempts, your defense is going to get hurt badly by hot perimeter shooting.

But Wisconsin won't have that problem. It's likely that opponents will improve their 3-point percentage against the Badgers the rest of the season, but because they prevent 3-point attempts so well and they force a lot of 2-point misses, their defense is still going to be one of the most effective in the land. It could be enough to keep Wisconsin on track for a decent seed in the NCAA tournament, even without much in the way of scoring punch.

Ken Pomeroy operates the advanced statistical site KenPom.com. Follow him on Twitter here.

FWIW, K-State's is 30.2% (#83). In league games its 29.3% (#2).

[mcmwcat]

argument for removing the 3pt line.  not really but i thought i'd throw it out there.  i guess the point is that you need to stop attempts from 3

[kso_FAN]

argument for removing the 3pt line.

Before the correction, I was going to point out that we already have a thread for comments like this one.

[Powercat Posse]

Pretty impressive numbers by Wisky.     2nd in the nation allowing only 23.3%  of opp shots to be beyond the arc,  and 4th in the nation allowing only 39.7% on 2 pt FG

Last 8 games when Ksu has tuned up its defense...................  Opp are taking 27.0% of shots from beyond the arc and only shooting 41.0% on 2pt FGs

[michigancat]

that was really interesting.

Explains a lot about why Frank's ball pressure defense is so effective, despite the backdoors and drives.

[kso_FAN]

This is Frank's 2nd best team for (full season stats) for 3PA% and best for 2PT%. Also his best defense.

It is an interesting correlation and one I wouldn't have suspected. Though when you think about it there is some sense to it. 3PT rate would be a somewhat similar principle to FT rate.

[michigancat]

This is Frank's 2nd best team for (full season stats) for 3PA% and best for 2PT%. Also his best defense.

It is an interesting correlation and one I wouldn't have suspected.

And that, my friend, is why Kenny Pomeroy is allowed to be the smuggest CBB writer in the game.

[kso_FAN]

This is Frank's 2nd best team for (full season stats) for 3PA% and best for 2PT%. Also his best defense.

It is an interesting correlation and one I wouldn't have suspected.

And that, my friend, is why Kenny Pomeroy is allowed to be the smuggest CBB writer in the game.

Yep. And I enjoy him greatly, no matter how smug (or no matter what MIR says).

[gatoveintisiete]

The difference in Wiscy's D and ours that has the most impact is fouls.

[kso_FAN]

The difference in Wiscy's D and ours that has the most impact is fouls.

I think that is offset by the fact that they don't force many TOs (which has more impact on games). The biggest difference is their eFG% is nearly over 4% better and their 2PT% defense is nearly 4% better.

[8manpick]

Didn't look at the stats to check KU, but I bet they are really high.  They are fantastic at closing out and bothering shooters that seemed like they were going to be open.

[gatoveintisiete]

The difference in Wiscy's D and ours that has the most impact is fouls.

I think that is offset by the fact that they don't force many TOs (which has more impact on games). The biggest difference is their eFG% is nearly over 4% better and their 2PT% defense is nearly 4% better.

I would argue that having your better players on the bench in foul trouble has a bigger impact especially when you have few offensive threats.

[mcmwcat]

 3PA/FGA conference play only:

offense:
mizzou is #2 (39.1%)
ksu is #6 (30.3%)

defense:
mizzou is #1 (27.5%)
ksu is #2 (30.3%)

[mcmwcat]

in the first game against mizzou they were 24/49 3PA/FGA.   ksu was 12/57

 

[Powercat Posse]

According to statsheet.......... we are #2 in defense in conf games on 3pt ratio 28.9%.   198 3PA/ 684 FGA.

Last 9 games it has been an amazing 26.8%

[mcmwcat]

corrected above.  thanks

[MakeItRain]

This is Frank's 2nd best team for (full season stats) for 3PA% and best for 2PT%. Also his best defense.

It is an interesting correlation and one I wouldn't have suspected.

And that, my friend, is why Kenny Pomeroy is allowed to be the smuggest CBB writer in the game.

Yep. And I enjoy him greatly, no matter how smug (or no matter what MIR says).

Credit when credit is due, still am not giving him my money

[mcmwcat]

baylor was 13/52 3pa/fga
ksu was 20/55

i'll take 7/20 every game please.

 

[kso_FAN]

Kenneth with more on 3PT defense...

How defense works: an investigation
02.22.12

The data from last Friday’s post has got me wondering about a lot of things and I hope it did the same for you. Mainly, how does defense work?

First, let’s try to noodle through an explanation of why a team would have no skill in affecting its opponents’ 3P%. If you are on offense, how do you decide when to take a three-pointer? Clearly, there’s some standard for launching a shot. No coach goes into a game telling his team, “we’re going to take 15 3-pointers tonight, regardless of what the defense gives us!” Players have a threshold for when to shoot.

On nights where the defense makes pressuring the ball a priority and de-emphasizes help defense, there will be fewer looks available that meet the average shooter’s standard. And on those nights, shooters aren’t going to take the same number of three-pointers they always do. Thus, a reasonable theory is that the quality of looks doesn’t change much from night to night.

Essentially what you get with defensive three-point percentage is this: When a shooter is open enough to shoot, how many threes do they make? When viewed this way, you can see why we have something close to a defense-free statistic here. I use that term specifically so that it’s analogous to its cousin term, “tempo-free statistic”. Consider these descriptions:

Points per possession: Describes how often a team scores when it has a chance (i.e. possession). This removes tempo from the qualitative assessment of an offense.

3-point percentage: Describes how accurate a team is from three-point range, given the opportunities it has to shoot. This removes the ability of the defense from the qualitative assessment of shooting ability.

The defense’s primary role in three-point defense is to limit the number of looks an opposing team gets. Perhaps saying that a team has no control over its opponents’ 3P% is a stretch. The obvious counter example would be Syracuse, who allows a lot of three-point attempts and generally keeps its opponents below the national average in 3P%. Maybe they have some skill, but keep in mind that the Orange typically play a weaker than average non-conference schedule, almost exclusively at home, and follow that up playing in a conference that historically does not have great shooters.

Over the last decade, here’s how the Big East ranked among the 32 conferences in 3P% during conference play: 25, 28, 24, 15, 24, 27, 23, 20, 22, 30. (Conference rankings now available to subscribers, BTW.) I have a feeling once we filter out the poor shooting ability of Syracuse’s opponents, we would find their affect on opponents’ 3P% is very small. Admittedly, it’s poor form to merely speculate on this, and I do plan to investigate this more thoroughly in the future.

Duke is probably a stronger counterexample, generally putting up good defensive 3P% (and 3PA%) numbers with half their schedule in a conference that occasionally has good shooter. And it stands to reason that a team’s standard for taking a three-pointer could change based on the opponent. If it’s increasingly difficult to score inside the arc as it is against Syracuse, then taking more difficult three-pointers is a reasonable solution.

For a team that is so suffocating on the perimeter like Duke, maybe shooters lower their standard out of the frustration of just wanting to take shots. Or perhaps teams like Duke and Syracuse that play from ahead the majority of the time enjoy the benefit of their opponents launching more questionable threes in order to catch up. It’s possible these factors exist. However, I think it’s clear from the data that these influences are a lot smaller than conventional wisdom allows.

But Ken, this cannot be right. Shooters obviously make more shots when they are wide open.

No argument here, but how many defenses are leaving shooters wide open very often? For any team, no matter how many attempts are allowed, opponents are taking a mix of wide open shots and contested shots and all flavors in between. Over the course of a few games the average quality of three-point shots tends to even out.

And no coach encourages his team to allow uncontested three-pointers. Actually, there might be one. Chattanooga coach John Shulman is going to go on the Mount Rushmore of wacky coaches (right next to Denver’s Joe Scott) when he retires because his team’s defensive stats suggest he coaches as if the three-point line doesn’t exist. Opponents have consistently taken nearly half of their shot attempts from beyond the arc and yet their 3P% is never terribly far from average.

People that are unaware of 3PA% (which is to say nearly everyone) are missing a very telling statistic that explains a lot of how defense works. It’s infinitely more useful than defensive 3P%, anyways. Can coaches use this to their advantage? I’m not sure, except to say that at first glance I think Shulman is crazy for running the system he does. However, I like having him around. The strategic diversity that college hoops offers is part of what make D-I hoops so much more interesting than the NBA to me. I tend to think K, Randy Bennett, and Rick Majerus have it right, but there are national-championship winning coaches (Jim Boeheim and Tubby Smith are two) that run systems that allow a high amount of opponents’ three-point attempts and I’m guessing they have good reasons.

There’s probably much more utility for this information to be used analytically than strategically. Tomorrow, I’ll publish some plots for other team stats to continue this perspective on how both defense and offense work. Would you believe that on a team level, offenses have surprisingly little control over their own 3P%?

[michigancat]

very cool catch by Ken.

[kso_FAN]

Kenneth with one more follow-up. There are multiple scatter plot charts, so it's difficult to put here.

Its pretty crazy that by the numbers 3pt shooting percentage is even more random than FT shooting percentage, but 3ptA/fgA is one of the most predictable shooting stats (both offense and defense) in basketball.

http://kenpom.com/blog/index.php/weblog/the_3-point_line_is_a_lottery/