Is there a Cost to Offensive Rebounds?

Helping or hurting?

Great minds think alike. Alex Konkel at Sports Skeptic also has a great take on this topic.

Recently, Henry Abbott wrote the following at True Hoop.

Offensive rebounds come with a cost

After reading this over, I contacted Henry with a few thoughts. And after a few e-mails, Henry asked me to write up a post with some of the stuff we were were talking about.

Let’s begin with part of what Henry had to say in the post:

Let’s say Doc Rivers told his bigs to crash the offensive boards more. They would certainly get more easy putbacks in particular and more field goal attempts for their team generally. More shots per possession. Better offensive efficiency overall.
But at what cost? How much would the team be giving up on all those possessions where the bigs didn’t get the rebound. That’s the most common outcome, right? In those cases, the bigs would simply not be back which hurts the team, for sure. Does it hurt the team more than now-and-again offensive rebounds are worth?
It’s a discussion for the ages, and it depends on personnel, opponents, element of surprise, opportunity and everything else.

With the discussion in hand, we now need to check the following links:

  • offensive rebounds and offensive efficiency (turning possessions into points, not zeroes or turnovers)
  • offensive rebounds and defensive efficiency (getting back on ‘D’ to prevent points and force turnovers)

We are testing if teams face a trade off when attacking the glass. Does getting the ball on offense hut you on defense?

Before we worry about that, I thought one should first look at some data.

We should start by noting that offensive rebounds clearly help your offense.  One can see that by looking at the formulation of offensive efficiency and the basic Wins Produced model.  So that part of the story seems clear.  But is there a link between offensive rebounds and the opponent’s efficiency?

One simple check is to look at the correlations between

  • offensive rebounds per possession and defensive efficiency (points surrendered per possession), or
  • offensive rebound percentage and defensive efficiency

And here is what you see (looking at team data from 1987-88 to 2011-12):

  • correlation between ORB per possession and defensive efficiency: 0.006
  • correlation between ORB percentage and defensive efficiency: 0.03

Neither of these is statistically significant.  So this simple test indicates that teams do not face a trade-off.   Offensive rebounds don’t appear to be related to an opponent’s scoring efficiency.

Now it may be that few teams try this strategy.  So perhaps we just need to check the few teams that have tried this.  Certainly we don’t see anything if we look at all teams.

Henry goes on to note a related argument.

You know which three teams got the fewest shots per possession last year?
Worst by a country mile was the Celtics. Second was the Thunder. Third was the Heat.
In other words a good chunk of the very best teams in the league, including both Finals competitors, simply don’t seem to place much of a priority on the offensive glass. Presumably those were the teams where opponents almost never got to start their attacks with big men struggling back down the floor after a failed attempt to grab an o-board. Presumably, it’s a hassle to miss out on those easy buckets.

I asked Henry to clarify his argument and he suggested there should be a link between field goals attempted per possession and winning.   To address this story, I looked at…

  • correlation between field goal attempts per possession and winning percentage: -0.01
  • correlation between shots per possession and winning percentage (where shots = fga + 0.45*fta): 0.15

The first correlation is not statistically significant while the second one – although quite small – is significant.  However, the second correlation is positive and that is not consistent with Henry’s argument.

In sum, it doesn’t appear teams should pass on offensive rebounds.  Teams win because teams are able to

  • gain possession of the ball (i.e. grab defensive rebounds and force turnovers)
  • keep possession of the ball (i.e. avoid turnovers and grab offensive rebounds)
  • ultimately turn possessions into points (i.e. shoot efficiently)

If you do those things, you win.   In other words, offensive rebounds are on the list of things to do if you wish to win.

Let me close by noting that offensive rebounds are not the only item on the list.  And a team could win without being particularly good at grabbing offensive rebounds.  For example, teams that shoot efficiently don’t have to worry as much about grabbing offensive rebounds because the ball is going in the basket.

That being said, it doesn’t appear that teams are hurt defensively by grabbing offensive rebounds.  So if those rebounds are available, it seems like a good idea to have someone on your team grab these.

- DJ

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