NBA Ultimate Questions: the Boston Celtics Rebounding Dilemma

The Offensive Rebounding Issue

Recently, our beloved editor Zach Warren made the point that the 2012-2013 Boston Celtics are historically notable in their terrible offensive rebounding. This is a common criticism of the Celtics and the numbers speak for themselves in this regard. They grab only 18.5% of offensive rebounds available. As a team, the Celtics average 7.2 offensive rebounds per game, only 1.4 more than Anderson Varejao does on his own.

According to Celtics coach Doc Rivers, however, this is not so much an issue of the players not executing as a strategic decision. He recently explained this to reporters after a lone Brandon Bass offensive board in the final minutes was the only thing that kept the Celtics from being held without a single rebound on that end of the floor. “That is a number I rarely look at, offensive rebounds. Statistically, it holds up. I can tell you, you don’t offensive rebound, you stop [the opponent's] transition, you win more games than when you get offensive rebounds. I can guarantee you that on those stats.” Challenge accepted Doc.

The Numbers Breakdown

First, props to Kevin Pelton on Basketball Prospectus for having taken a look at transition defense last year and developing the transition metric I’m about to use. Basically, using Synergy Sports, it’s possible to look at the percentage of transition plays a defense allows and how efficient they are at defending these plays as compared to an average play on a points-per-play (PPP) basis. Multiplying these two figures together gives a measure of transition points given up per 100 plays. One might expect that since the Celtics are on pace to be the worst offensive rebounding team in history and have been one of the NBA’s elite defensive teams since Kevin Garnett arrived, they would be pretty solid in this metric. The reality is that with a mark of 5.8, they rank ahead of only Cleveland – a team who is, of course, terrible at pretty much everything.

The problem is not transition opportunities, as the Celtics allow fewer fast breaks than any other team in the league at only 10.6% of their defensive plays. Boston’s transition woes are the result of poor defense on these plays. Teams in transition against the Celtics score 1.42 points per play, putting the Celtics easily in last place in this stat. For context, an average play so far this year scores about 0.87 points and the average transition play scores at a 1.13 PPP clip. Despite everyone’s best efforts to get back as soon as the shot is released, the Celtics are quite terrible at stopping other teams unless their defense has time to get completely set.

The Celtics are not an outlier in that their dedication to avoiding offensive rebounds hasn’t paid off. In fact, the correlation between offensive rebound rate (ORR) and defensive efficiency (-.06) as well as the correlation between ORR and the aforementioned transition metric (-0.09) are insignificant. These numbers alone do not prove that the Celtics are making the wrong choice. There is some correlation between the percentage of transition plays allowed and ORR (0.37). It is possible that this Celtics roster is inherently bad at stopping transition plays and the decision to get back in transition limits transition chances, preventing the Celtics from giving up even more points to transition.

Given that the Celtics are already among the worst in transition defense, a change in philosophy on offensive board crashing can’t do much damage. More likely, the added offensive opportunities from the rebounds would make the Celtics a better team overall. There’s not even any reason to assume they would get significantly worse in transition defense. It’s quite possible to commit to offensive rebounding and still defend well, even in transition. Frankly Doc, I feel mislead.