Rebound Rates—A Commentary by Ian Ayres ’86
The following commentary was published in The New York Times on June 23, 2008.
By Ian Ayres ’86
The Celtics’ demolition of the Lakers reminds me that the sport announcers would do well to put more emphasis on “rebound rates.” Like putt probabilities, the rebound rate basically tells you the probability that a team will get the next rebound.
Can you answer a fairly simple question: In the NBA if a team misses a shot, what is the probability that it will get the (offensive) rebound?
Most people I’ve asked think the probability is 10 percent or less. But it’s closer to 30 percent.
Game six was extraordinary not just because the Lakers had only two offensive rebounds, but because they shot so poorly (42.2) — so there were plenty of misses to rebound — and had only two offensive rebounds. As the great John Hollinger summed up:
[F]or the game [Los Angeles] had only two compared to 34 defensive boards for Boston. That’s a 6 percent rebound rate if you’re scoring at home; normally the offensive team gets around 30 percent.
One question that occurs to me is whether Lakers’ low number of offensive rebounds was just a matter of bad luck. If you have a 34 draws and if each draw has a 30 percent chance of success, then just by chance you might only have 2 successes. But a little analysis (using the same methodology that I used here to analyze political polls) suggests that we can reject the bad-luck hypotheses. The observed rebound rate of 6 percent is more than 3 standard deviations away from 30 percent — so there is less than a 1 percent chance that it would have occurred by chance.
Of course, just as the putting probability turns on the place on the green, the expected rebound probability turns on where the shot is taken and other factors. The website 82games.com gives a strategy for making the rebound probability turn on additional factors.
But even simple rebound rates can let us see things about the game for the first time.
1. This season Philadelphia had the highest probability of rebounding one of its own misses (31.8 percent), while Miami had a league last probability of 22.1 percent. Almost a 10 percent difference in getting the ball back when you miss can have a huge impact on games.
2. Rebound rates give you a better sense of who are the best individual rebounders. During the playoffs, Tim Duncan had the most defensive rebounds per game:
But Marcus Camby had a much higher probability of grabbing a defensive rebound. Camby himself grabbed more than a third of the other team’s misses:
3. Finally, rebound rates show that the art of the offensive rebound is distinctly different than the art of the defensive rebound.
Camby and Duncan, for example, rank only 35th and 21st among players in the playoffs in terms of offensive rebound probabilities. Who has a high offensive rebound rate?
Dwight Howard had the best playoff probability (16.9 percent), but the Celtics’ Leon Powe is close behind grabbing 15.2 percent of the Celtics’ misses. Of course, readers of this blog shouldn’t be surprised at Powe’s success.