Why corner threes matter for defenses

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The Spurs are holding teams to 36 percent shooting on corner threes this season after yielding a league-worst 47 percent last season. (Christian Petersen/Getty Images)

It has become accepted among NBA geeks that the hierarchy of the “best” shots, from most efficient to least, goes something like this:

1. Dunks/layups

2. Free throws

3. Corner three-pointers

4. Other three-pointers

5. Mid-range shots

Teams last season shot 39 percent on corner threes, which is about the same percentage teams shoot overall on two-pointers outside the restricted area. Teams last season shot about 35.5 percent on all three-pointers, meaning they shot something like 33.5 percent to 34 percent on three-pointers taken anywhere but the corners.

In short: The corner three is a great shot, something Spurs coach Gregg Popovich understood probably before the Internet became a thing.

Basketball is a game of finite possessions and close scoring margins. It matters if a team’s defense can chase shooters off of corner threes a couple of times per game, and limit those shooters instead to floaters or some other shot that is a) difficult and b) counts for only two points if it goes in.

Last week, I noted one reason the Clippers have ranked among the bottom 10 defensive teams this season: Opponents are shooting the lights out (about 44 percent) on corner three-pointers. The league was kind enough to send me data on opponent corner threes for every team over the last two seasons (through March 27), and I sent that data along to a two stats-savvy readers (Eric Maroun of the long-excellent Hardwood Paroxysm and Aaron McGuire, the latter of the fantastic blog Gothic Ginobili). Those guys then measured how strongly defending the corner three correlates with overall defense and team winning percentage.

The answers are interesting, if incomplete. A few general findings before we get to the team level:

Limiting attempts seems to matter more than the percentage of corner threes opponents make. That’s not surprising. Lots of studies have found that limiting raw three-point attempts matters more than opponent three-point percentage. The raw number of corner-three attempts allowed last season correlated more strongly with both winning percentage and overall defensive rating than shooting percentage on corner threes, according to work by Maroun and McGuire. It also correlated more strongly with winning percentage than a team’s defensive rebounding rate and the rate at which a team forced turnovers. (In general, the correlation between defensive rebounding and winning percentage is typically stronger than it was last season, according to historical data.)

In general, the amount of corner threes a team allowed last season correlated strongly with winning percentage as a few other key factors have done so in prior years, including how often a team allows and earns free throws.

Last season’s Rockets (41.9 percent allowed on corner threes) and Spurs (a league-worst 47 percent) both survived defensively in part because they ranked second and fourth, respectively, in the number of corner-three attempts they permitted.

Overall last season, the average team attempted 412 corner threes. Of the 12 defenses that allowed fewer than 412 corner-three tries, nine ranked among the league’s 15 stingiest defenses overall. That group included the Bulls and Celtics, the league’s two best defenses. And of the 12 teams that allowed the most corner-three attempts, only one — the Lakers — ranked better than 17th in points allowed per possession.

There are exceptions, obviously, and this season’s Clippers are an example of how damaging even an average number of corner-three attempts can be if a large chunk of them are wide-open looks. And last season, five of the league’s 10 stingiest defenses, in terms of points allowed per possession, allowed an above-average number of attempts from the corner: the Heat, Magic, Grizzlies, Hornets and Lakers. But four of those teams — all but the Lakers — allowed a number of corner threes close to the league average. Yielding a lot of such shots was generally bad.

Chicago is ridiculous. The Bulls through 49 games this season had allowed 140 corner-three attempts. The Sixers, through that same stretch, had allowed the second-fewest — 192. The gap between Chicago and Philly is the equivalent of the gap between the Sixers and the league average for corner-three attempts allowed. Chicago opponents are attempting just 2.85 corner threes per game; the average team attempts about five per game.

Guess who yielded the fewest corner-three attempts last season? The Bulls, with a total of 305, or about 3.8 per game. They have shaved a full attempt off that number this season. Tom Thibodeau is scary.

We might be seeing the impact of coaching here in lots of cases. Rick Adelman, for one, appears to be a huge difference-maker in terms of defending the corner three. The Timberwolves allowed a league-high 511 corner-three attempts — about 6.2 per game — last season under Kurt Rambis. Under Adelman, the Wolves have allowed about 4.3 corner threes per game, the fifth-lowest amount. They are playing at a slower pace this season, but the decline — about three possessions per game — does not come close to explaining the drop-off in corner threes on its own.

This is especially so when you look at Adelman’s former team, the Rockets. Houston last season allowed the second-fewest corner-three attempts, trailing only the Bulls, but they’ve allowed more than average this season. In fact, the Rockets are on pace to allow about 30 more corner three tries in this 66-game season than they did in the full 82 last season.

In what probably amounts to a heavy dose of good luck, the Wolves have held opponents to 28.4 percent shooting on corner threes this season. That is unsustainable, but perhaps another sign of how much Adelman emphasizes contesting this shot.

Doug Collins’ Philladelphia team, filled with rangy and quick athletes, has effectively shut down the corner three for two years running. Only Chicago has allowed fewer such shots combined over the last two seasons, and Philly opponents have shot below the league average from the corner in both seasons.

Another coach to watch: Lawrence Frank. The Pistons are right behind Philly in corner-three attempts allowed after surrendering many more than average last season while playing at a tortoise-like pace. Frank, of course, is a defense-first coach who spent 2010-11 with the Celtics, a team that patrols the corner well.

Likewise, the Lakers are allowing about 1.2 fewer attempts from the corner this season under Mike Brown.

Luck may play a part. It would be interesting to spend a bit more time with these numbers to see how much teams can really control opponent shooting percentages from this spot. League observers ranging from Phoenix coach Alvin Gentry to Basketball Prospectus genius Kevin Pelton have argued that random luck plays a fairly large role in three-point percentage against, as evidenced by how the same stat often varies hugely from year-to-year on teams that undergo very little roster turnover.

San Antonio, for instance, is holding teams to 36 percent shooting on corner threes this season after yielding that ghastly 47 percent figure last season. Is that luck, or has Popovich’s club sharpened its focus?

  • Published On 3:45pm, Mar 29, 2012
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