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The Death of Rebounding Differential

Raw rebounding is one of those tricky statistics. A guy can look dominant in a game that features many missed shots and pedestrian in a game that doesn't. Extended to the team level, rebounding margin (total rebounds - opponent total rebounds) can often hide the full story as well.

As John Gassaway notes for Basketball Prospectus, the very concept of rebounding differential is dying a slow death at the college basketball level:

One year ago this week I penned a piece under the winningly accommodating let’s-all-be-friends headline "Rebound Margin Must Die." The inciting incident behind my urgent call to arms was a major-conference head coach crowing on Twitter that his team was ranked in the top 30 or 40 or something nationally in rebound margin.

I had no contact with that coach, I simply retreated to my lair and wrote RMMD. Nevertheless, within 40 minutes of hitting "post" I had a DM in my Twitter inbox from that very same head coach:

Good read regarding rebounding margin. You bring up some interesting points, and agree with several, though not all.

And I knew then that the forces of light and reason had triumphed over darkness and "plus-12 advantage in rebounds."

The clear substitutes for raw rebounding numbers are, of course, rebounding percentages. Defensive rebounding percentage (DREB%) is the percentage of all opponent misses that a team collects. If an opponent misses a ton of shots? No problem- the team may collect a large number of defensive rebounds, but the percentage should stay constant. The same is true on the offensive end; if a team makes most of their shots, then OREB% won't penalize them for not grabbing as many total offensive boards.

What are the downsides of OREB% and DREB%? The big one is obviously the issue that plagues all rate statistics. Success in the NBA should be equal measures quantity and quality. Rebounding percentages measure quality, but they don't differentiate between a guy putting up 20% DREB for 20 minutes and a guy doing it for 40 minutes. While rebounding percentages stay very consistent across large minute fluctuations, someone pulling down more rebounds in more minutes at a slightly lower rate won't be acknowledged as he should be. But ultimately, once we correct for players that simply aren't out there enough (going by "qualified for rebounds title" is a decent way to filter for this), rebounding percentages are absolutely the way to go.

As of today, the Hornets' leading offensive rebounder by OREB%- Jason Smith- ranks 78th in the league. This should come as no surprise, as the Hornets pull down just 23.6% of their own misses- the 6th worst mark in the league. Interestingly, the four teams worse than New Orleans at offensive rebounding- Dallas, Boston, Indiana, and Denver- are all playoff teams. 

On the defensive side, Emeka Okafor, Trevor Ariza, and Chris Paul all rank among the top DREB% practitioners at their respective positions. As a result, New Orleans pulls down 77.7% of all opponent misses- the second best mark in the NBA. The Hornets' conference leading defense is largely fueled by their defensive rebounding ability.

Hopefully it's only a matter of time before the concept of "rebounding differential" vanishes from NBA telecasts and analysis as it has from the college ranks.