How defense works: an investigation
02.22.12
[Note: the graphs originally posted Friday were slightly in error. The corrected data has been posted and does not change the conclusions drawn. My apologies for the mistake.]
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%?
Defense has little control over opponents’ 3P%
02.17.12
I took last season’s conference-only data for every team and split it into two halves. Then I compared each team’s opponents’ 3P% between the first half and second half of the conference season. I did the same for opponents’ three-point attempt percentage (their percentage of field-goal attempts that are from three-point range). The following plots of that data should make it clear that opponents’ three-point accuracy is largely out of a team’s control.
Play-by-Play Theater: Longest foul-free streak
02.16.12
In this edition of Play-by-Play Theater, we investigate how long a team can possibly go without committing a foul. Let’s face it, committing fouls can be fun. Just ask Texas Tech! As with eating candy, it’s quite difficult to go long periods without just hammering an opposing player trying to advance the basketball towards the basket.
Last Thursday, New Mexico State did not commit a foul between the 2:25 mark of the first half to the 6:24 mark of the second half, a span of 16:01. Tweeter @wothism thought that might be some sort of record.
Well, our tweeter mistakenly thought the foul-free stretch was longer than it was, but even had it been 18:48 it still would not have cracked the top ten in my play-by-play database.
There have been 16 cases of a team going at least 20 minutes without committing a foul in the 15,066 games for which I have data over the past three seasons. The record-setting occurrence took place on March 7, 2011. The site of this incredible feat of restraint was Webster Bank Arena in the title game of the Spark Energy MAAC Championship.
The combatants were the fourth-seeded Saint Peter’s Peacocks and the second-seeded Iona Gaels. Only, the Gaels spent a long time not engaging in combat. At 11:44 of the first half, Kyle Smith committed Iona’s third, and last, team foul of the first half. The Gaels kept it rolling after the break, not picking up their first foul of the second half until Rashon Dwight’s infraction with 8:02 left. In total, there was a whopping 23:42 of game time between whistles against Iona. Take a bow, Gaels. The bad part is that Iona was outscored 28-23 over that time and saw a four-point deficit grow to nine. They would ultimately get upset and fall 62-57. (PBP)
Coincidentally, Prairie View made a run at the record on Monday against Grambling, going from 9:04 in the first half to 6:16 in the second half between fouls. The Panthers committed just eight fouls in the entire contest enroute to the easy win over the nation’s worst offense. Definitely no need to send Grambling to the line.
Here are the five longest foul-free streaks over the past three seasons…
03/07/11 23:42 Iona vs. Saint Peter's 02/13/12 22:48 Prairie View vs. Grambling 12/17/10 22:09 Ohio State vs. Tennessee Martin 03/10/11 21:49 Penn State vs. Indiana 02/05/11 21:47 San Diego State vs. TCU