Monday, December 7, 2009
Only so many rebounds to go around?
By Kevin Arnovitz
In one of his journal entries last season, the Clippers' affable young center, DeAndre Jordan, joked that Marcus Camby would occasionally give him the stink eye when Jordan collected a rebound in Camby's proximity. Jordan's comment was a light-hearted window into on-court dynamics, but the story also speaks to one of the tougher basketball questions statistical analysts have to confront, one that Jon Nichols explores at Hardwood Paroxysm:
One thing many people have wondered is whether or not there are diminishing returns for rebounds. Basically, what that would mean is that not all of a player’s rebounds would otherwise have been taken by the opponent; some would have been collected by teammates. Therefore, starting five lead leaguers in rebounds would probably be overkill because eventually they’d just steal them from each other. At some point, there are only so many rebounds a team can grab, and some are just bound to end up in the hands of the opponent.
In other words, does playing with a rebounder like Marcus Camby diminish the rebounding numbers of DeAndre Jordan (or any of Camby's other teammates, for that matter)? And if so, how can we tell?
Eli Witus explored how the laws of diminishing returns govern basketball in a series of posts at Count the Basket a couple of years ago. In the second post in the series, Witus concludes that, when it comes to defensive rebounding, evidence of diminishing returns exists.
Nichols uses a slightly different criteria for the lineups he selected for his study, but his conclusions weren't dissimilar from Witus' study: "[T]here is a much stronger diminishing returns effect at play with defensive rebounds than there is with offensive rebounds."
In other words, there isn't much theft among teammates for offensive rebounds. A player who grabs a ball off the offensive glass isn't likely to be depriving another guy on his team that rebound. But defensive rebounds are another story: Put a bunch of players who have exceedingly strong defensive rebounding rates on a 5-man unit together and individual rebounding rates are likely to suffer because there simply aren't enough defensive rebounds to go around.
Nichols looks at a bunch of interesting data -- home/road splits for rebounding rate, as well as assists, blocks, steals. The post is well worth your time.