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December 17, 2009
Rebound Margin Must Die

by John Gasaway


If you're a regular reader, you know where I stand on (ugh) "rebound margin." Maybe you're even rolling your eyes and thinking, "There goes old man Gasaway again, out on his porch and shaking his cane at the whole hoops neighborhood: 'Consarnit, rebound margin is eeevilll! Someone fetch me my liver pills.'" Believe me, I don't like still having to do this in 2009.

I guess what pushed me over the edge was seeing a major-conference coach rejoicing on Twitter a week or so ago that his team was in the top 30 or 40 or something in the country in (gack!) "rebound margin." The coach's tweet got to me like fingernails on the blackboard for a couple reasons. One I was shocked that at this late date any head coach would still be thinking "rebound margin" (grrr) has any meaning whatsoever. (Or at least that his Prospectus-reading assistants wouldn't intercede politely and gently lead the Boss away from the old girl.) Two I was even more stunned that this far into the 2000s any organization would still be tracking this unicorn of a stat. In fact as long as we're still using (sigh) "rebound margin," we might as well see what phrenology can tell us about the top 25. Because to my eye John Wall's brain pan shows a very high predisposition toward dunkitiveness. What do you think?

For the purposes of killing the term I actually looked up the national leaders in you-know-what. According to the NCAA's official stats, Tulsa currently leads the nation in, uh, that thing. Fine. Know what? The Hurricane do indeed rebound the ball very well, thanks in large part to the contributions of seven-footer Jerome Jordan. Doug Wojcik's team is particularly strong on the defensive glass, where so far this season they've hauled down no fewer than 77 percent of their opponents' misses. That is an incredibly high number that is poised to climb even higher, with Tulsa slated to play Jackson State tonight. If this keeps up, which it probably won't, you can put this team up there on the same beastly rebounding bleachers with Michigan State 2000.

There. That's a reality-based account of the Hurricane's excellent defensive rebounding, one that acknowledges that the world is round, grape juice stains things, and a breakfront is a piece of furniture that breaks in the front. But look at the completely non-rebounding factors that come into play when you calculate something as vaporous and ersatz as (aaiieee!) a "rebound margin." A huge factor in Tulsa's sheer number of defensive rebounds (as opposed to their laudably large share of the available boards) is the fact that they never force turnovers. Ever. More than 85 percent of opponents' possessions end in either a FG attempt or free throws. Lesson one: "Rebound margin" (shudder) penalizes defenses that are good at creating turnovers.

Then there's the much larger issue entailed in any tallying of mere rebounds. I don't want to freak anyone out here, but I have long been of the opinion that there is no such thing as "rebounds," per se. There are only offensive rebounds and defensive rebounds, and they are completely separate and qualitatively different animals.

A defensive rebound is an unalloyed good. Every team in the country wants defensive rebounds. You will never hear a coach telling his team, "Men, don't worry about defensive rebounds. Just let the other team keep shooting. We'll get the ball back anyway once they score." Therefore the closest thing to a synonym for "rebounding" is simply how well a team does on the defensive glass. Prowess on the defensive boards is an open and fair competition because every team wants to be good at it. (Open and fair among teams, less so among players. If your team plays man defense and your coach tasks you with guarding a perimeter threat, your individual defensive rebounding percentage will suffer.)

Offensive rebounding is a whole different ball of wax. Some coaches choose to go after offensive boards. Tom Moore certainly does. His Quinnipiac team currently sits atop the (actual, correct) national offensive rebounding leader board, recovering a notably robust 45 percent of their own missed shots. Voracious offensive glass-eating Bobcats, I salute you!

Then again other teams prefer to do without offensive rebounds. Whether it's because they run a perimeter-oriented offense that puts lots of shooters out around the arc, or because they think it will help their transition defense, or both, a healthy minority of coaches plainly de-emphasizes offensive rebounding. Bo Ryan has often displayed this de-emphasis at Wisconsin, and no one can accuse his teams of being weak on the glass. The Badgers simply elect not to run the risk of giving up an easy basket on the other end. Lesson two: "Rebound margin" (choke, gasp) penalizes teams that choose not to go after offensive rebounds.

Which brings us down to the blindingly obvious and indeed fatal flaws with this thing: Pace and misses. Teams that play fast-paced games with lots of misses, both their opponents' and their own (see the problem already?), will rack up a high number of rebounds. But of course there's nothing about a faster-paced team that truly makes them a better rebounding group than a slower-paced outfit. And since when should you actually need to miss your own shots to look "better" statistically?

Again, look at Tulsa. Playing at a somewhat fast clip, they force opponents into a ton of misses because Jordan is having a great year in terms of shot-blocking and shot-altering. So far so good. At the other end of the floor Wojcik's team is OK but not especially lethal at shooting the ball. Note that if they were just a little more accurate with their own shooting, however, they could tumble off the pinnacle of this national "rebound margin" (erk!) list. (Assuming, of course, that they are indeed getting the offensive boards when they miss. Otherwise those misses will help the opponent's you-know-what.) Better shooting and more points can mean you do worse on this metric. Nice stat you have there.

Look, the next time you see this particular two-word abomination, keep in mind this is what it's really measuring:

"Team that plays at a moderately fast pace and never forces turnovers but does force a lot of misses and rebounds them and then comes down the floor and misses a fair number of their own shots and rebounds those at some risk of giving up transition baskets by the opponent."

If you want to track that, be my guest. Otherwise:

Defensive rebound percentage = defensive rebounds / (defensive rebounds + opponent offensive rebounds)

Offensive rebound percentage = offensive rebounds / (offensive rebounds + opponent defensive rebounds)

The new decade is a blank slate, the time is now, and the Twitter hashtag is #unicornstat. Si se puede, etc.

Note to regular readers: And I swear (insert Vito Corleone voice here), on the souls of my grandchildren (which I'll have in 30 years), that I will never speak of this again.

John also shakes his cane and rambles on with splenetic rants on Twitter: @JohnGasaway. College Basketball Prospectus 2009-10 is now available on Amazon.

John Gasaway is an author of Basketball Prospectus. You can contact John by clicking here or click here to see John's other articles.

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Louisville's Early Str... (12/16)
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Around the Rim (12/17)

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