First, we have to realize something that seems counterintuitive. Players rebound the same way, unless they have a teammate on the team who is a high impact rebounder. In short, team rebounding has little impact on individual rebounding. Once a team gets a to a certain point, players cannibalize rebounds from their own teammates--but if you're a good rebounder, you still get your share. Proof? Here are spreadsheets that show 89 seasons from top rebounding C/PFs.
http://docs.google.com/Doc?docid=0AQlwu ... bWZq&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... eGdr&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... a3Zo&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... c2Qz&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... dGN3&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... NmR0&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... Y2c3&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... Jkbg&hl=en
http://docs.google.com/Doc?docid=0AQlwu ... RndA&hl=en
In those 89 seasons:
There were about 33 seasons where the player played on a team that rebounded better or worse than his usual teams, and the player's rebounding moved in the same direction. Great Rebounding Team = Great Rebounding Year; Bad Rebounding Team: Bad Rebounding Year. This shows a positive correlation between team rebounding and individual rebounding.
There were about 32 seasons where the player played on a team that rebounded better or worse than his usual teams, and the player's rebounding moved in the opposite direction. Great Rebounding Team = Bad Rebounding Year; Bad Rebounding Team: Great Rebounding Year. This shows a negative correlation between team rebounding and individual rebounding.
There were about 24 seasons where the player played on a team that was equivalent to his normal rebounding team, AND/OR rebounded almost exactly as he was supposed to. This shows a neutral correlation between team rebounding and individual rebounding.
You could go a step further and break down the neutral numbers, but you end up with the same thing. There's no correlation between team rebounding and individual rebounding.
So what happens when a team has all good rebounders? Who loses out? The rule is simple. Great rebounders get their rebounds. When the team starts to hit the high point of the ceiling, they cannibalize from their own players. Great rebounders take rebounds from lesser rebounders—the team is less important. Impact rebounders, the best of the group, always get their rebounds.
Let's look at a more recent player—Zydrunas Ilgasukas. He's a starting C that, since 2003, has played 65-81 games a year.
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Year Reb % Team Reb%
2003 14.1 52.1
2004 14.2 52.0
2005 15.2 52.0
2006 15.3 52.0
2007 16.4 52.7
2008 17.5 53.1
2009 16.5 51.1
2010 15.5 50.8
Well...wtf? The Cavs have always had good rebounding teams. When they got better in 2007 and 2008, Big Z's numbers went up/ When the team rebounding numbers went down in 2009, his Reb % went down too (although it was still over his average of 15.5 for that period). This year, on the worst rebounding team he's been on in the last eight years, he'd bang on his average. So—team rebounds well from 2003 to 2006; Z's rebounding slowly increases. Team rebounds really well in 2007 and 2008; Z's rebounding goes up. Team rebounds worse in 2009 and 2010; Z's rebounding declines.
In this case, there's more of a positive correlation than a negative correlation. The better the team rebounds, the better Ilgauskas rebounds. There are a couple of players like this. There are a couple of others that show negative correlation. Taken as a group, they balance out. The team has little to no effect on individual rebounding.
Other than natural up and down movement—what affects rebounding? Impact Rebounders. An impact rebounder is a player that rebounds 5.5 to 6% higher than an average player at his position. Given that the average Reb % for NBA starters by position are something like
C/Primary Frontcourt Rebounder—15.5%
PF/Secondary Frontcourt Rebounder—13.5%
it's pretty rare to have an impact rebounder. Dwight Howard is there. Not many others.
To give you an idea of the impact of a player like this, a 5.8% difference in rebounding for a player that plays 37 mpg is huge. It's shocking. At 41.5 rebounds per game, it looks like this
One player is responsible for a difference of 300 rebounds a game...essentially, turning a poor rebounding team (-100 rebound differential) into an outstanding rebound team (+200 rebound differential). That's the impact that Magic Johnson, in this example, had.
The problem with rebounding—but, at the same time, the thing that makes it a fascinating stat to analyze—is that there is a fixed number of rebounds and the difference between being a good and poor rebounding team is so low. Let's say that your starting SF grabs 6.5 rpg, when the “average” SF gets only 5.7. And your backup PF/C, who is supposed to get 4.2 rpg, gets 4.6 rpg. Everyone on the team is average. The immediate assumption is “well, that won't make a whole lot of difference.” You are in the upper third of teams in rebounding because of those small differences. In other words, there';s not a lot of movement available for rebounding.
So what does this mean? Well, on the most basic level, it means you can't stockpile rebounding. Once you get to a certain point—about 53% of available rebounds--you're topped out. After that, players will cannibalize from one another. What this seems to indicate, is that the better rebounders will maintain their numbers at the expense of the lesser rebounders. So if Marcus Camby changes teams, he's still going to rebound at an elite level.
Let's look at a good rebounder who got brought down by a great rebounder. If Dennis Rodman joined the San Antonio Spurs in 1994—which, by coincidence, he did—we can speculate that he'll take rebounds from the rest of the team. The Spurs were already a good rebounding team. But there's an upper limit to how good you can be, and it's pretty much Darwinian among teammates. Rodman's Reb % didn't suffer with the Spurs. David Robinson's did. Here are Robinson's numbers and his team's numbers from 1990 to 2001.
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Year Reb % Team Reb%
1990 18.5 51.5
1991 19.1 51.8
1992 17.7 52.0
1993 17.1 49.0
1994 14.8 53.0
1995 16.2 51.6
1996 18.4 48.7
1998 18.2 51.4
1999 17.8 49.9
2000 17.1 50.4
2001 16.5 50.4
The Spurs are one of those teams that using Four Factors Rebounding percentages really messes with. I think they're a better rebounding team than this. But let's look at this. The first Spurs teams David Robinson every played on were among the best rebounding teams he played on. And he was pretty much at his peak as a rebounder. In 1992, the team was again a very good rebounding team—and Robinson's rebounding numbers went down. Okay...negative correlation. Then, in 1993, the team's rebounding dropped significantly—but so did Robinson's rebounding performance. The 1996 team was as bad as the 1993—but Robinson rebounded great. The 1998 team was another good rebounding team—and Robinson's rebounding stayed the same and was above average for him. You get the point. 1990-3, and 1996-2001, there's no connection between how the Spurs rebounded and how Drob rebounded.
So why are things so nuts in 1994 and 1995? The Spurs were at their absolute peak as a rebounding team in 1994, and Robinson was awful that year by his standards. They were very, very good in 1995...but Robinsons's rebounding was astill very low for him. Much lower than it had been in 1991 and 1992, when the team rebounded better. Much lower than in 1990 or 1998, when the team rebounded just as well. What caused the odd drop in David Robinsons's rebounding in those two years? Dennis Rodman did. David Robinson's rebounding wasn't affected by how his team rebounded....it was only affected when he played with a guy who was a better rebounder than he was.