Wednesday, January 19, 2011

Over The Back? What Over The Back? [Or: Minute-Adjusted Tempo-Free Rebounding Leaders]

[EDIT: I made a mistake in the original description of how to calculate OffReb+. I originally wrote that I multiplied by 70.2, but that’s incorrect. 70.2 is the average total rebounds in a game, for both teams, so I actually multiplied by half that (35.1) when I did the calculations. I just had a senior moment when I wrote it out.  Sorry about the confusion. The reason I noticed in the first place is that Mike Rogers over at The Only Colors has a couple nice posts up that expand on this idea (here and here).  Highly worth checking out.  I noticed his numbers didn’t jive with mine, and that’s how I spotted the error in the text.  So, thanks Mike!]

In case you missed it, Tennessee’s Brian Williams made what ESPN calls a “falling over-the-back buzzer beater” last night against Georgia. Bulldog Chris Barnes did a good job of boxing out, but Williams simply reached over his shoulder and snatched ball. The play reinforced a thought that’s been rolling around in my head: that instead of merely praising players with high offensive rebounding rates (whether measured by raw numbers or by offensive rebounding percentage [OR%]), we ought to be praising those that can do it without fouling. It’s not that the fouls themselves are so detrimental – if a player dials back the physicality enough to prevent the foul, he likely prevents the offensive rebound as well. But racking up fouls on high-risk offensive boards leads to reduced minutes for a player that provides at least some value in the form of rebounds.

Take a look at the current top ten offensive rebounders, by OR%, along with their fouls committed per 40 minutes (FC/40). Over half of these guys would foul out if asked to play play 40 minutes:

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Hey, look – Brian Williams!

I thought it would be interesting to look at top ten that takes minutes played into account. This should penalize the foulers, plus it should knock out any small sample size wonders.

So, here’s what I did. From team stat pages on kenpom.com, I see that centers account for 32.7% of offensive rebounds, and power forwards for 29.3%, with a steep drop off after that. I chose 30% as the share of team offensive rebounds for an average C/PF. Combining that with the average team OR% of 32.6% gives me a typical big man OR% of 9.8%. Subtracting that from a player’s actual OR% gives his OR%-above-average. I multiply that by 35.1 (half of the average number of total rebounds in a game this year according to StatSheet) to get his adjusted offensive rebounds above average, per 40 minutes. This number then gets multiplied by his percent of team minutes played, and I’m finally left with a value that represents the number of offensive rebounds the player gains you per game, over an average big man, assuming his typical playing time, in a game which has an NCAA-average number of rebounds available. I’ll call it OffReb+.

Here’s the OffReb+ top ten:

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It’s never a surprise to see Kenneth Faried top any list relating to rebounding, but his lead here is huge. Nobody else comes close to combining his OR% with a low foul rate and high minutes played.

Look how far Rhamel Brown rose, just by being able to stay on the floor for significant minutes.  Also note that a lot of low-minute guys are still on here, partly because there just aren’t many players that can pick up offensive rebounds without fouling.

To look at defensive rebounding, I used the same logic as above, but plugged in the appropriate defensive rebounding numbers, and come up with a DefReb+ top ten:

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There’s Kenneth again, though with a smaller lead. That makes sense – when some teams don’t even bother to crash the offensive glass, everyone will do well against them, making the top talents stand out less.

This list doesn’t suffer at all from the fouls problem that plagues the offensive rebounding leaders, which also makes sense – defensive rebounding is generally considered to be about maintaining established position, instead of the aggressively trying to overturn that positional hierarchy. With one guy standing still, and one guy trying to go around or through him, who’s going to end up on the right side of the whistle?

Well, last night it was the guy going over the back, but you get the idea.

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