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How B/R's New Rebounder Rating Proves Not All NBA Boards Are Created Equal

Kelly Scaletta@@KellyScalettaFeatured ColumnistSeptember 12, 2014

Los Angeles Clippers center DeAndre Jordan (6) looks towards the basket while defended by Detroit Pistons forward Kyle Singler (25) and Andre Drummond during the second half of an NBA basketball game in Auburn Hills, Mich., Monday, Jan. 20, 2014. (AP Photo/Carlos Osorio)
Carlos Osorio/Associated Press

Rebounds, unlike men, are not all created equal, and Bleacher Report's new Rebounder Rating proves it. 

As a statistical measure, rebounds can be misleading. On the surface, they’re all the same—it's just grabbing a missed shot. But some are harder to get than others, and the box-score numbers don't reflect that. 

My Bleacher Report colleague, Adam Fromal, and I developed a new way to look at rebounds. We call the result "Rebounder Rating." In a sentence, Rebounder Rating is a measure of how many rebounds per game a player would be expected to gather if every opportunity were contested.

His article ranks the rebounders; mine breaks down the primary takeaways.

Two Different Kinds of Rebounds

Consider two scenarios:

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In the first, a player is running down the court on a fast break with his teammate trailing him. The opposition concedes the points and doesn’t hurry back. The breaker misses the layup, but his teammate—the only other person on that half of the court—tips it in.

In the second: A rebounder goes up into the trees and fetches a missed shot, yanking it from the hands of three opponents.

These two things are not the same, but they are treated the same. Just looking at rebounds doesn't differentiate between how the rebounds were obtained—it only records that they happened.

Does getting the rebound when no one else is there to grab it count for something? Actually, it should. The player in our hypothetical scenario made the decision to trail. Everyone else conceded the layup. Making the effort to get in position to grab a rebound worth something.

However, it shouldn't count as much as if he’d grabbed the rebound away from other players.

Thus, there are two types of rebounds: contested and uncontested. NBA.com's SportVU makes this distinction, but it doesn't advance it.

Rebounder Rating identifies the difference and credits each appropriately in one overall number.

How Rebounder Rating Addresses the Problem

How do we do that? The tracking data provides three numbers that can help us: rebound chances per game, uncontested rebounds per game and contested rebounds per game.

First, we made the assumption that a player gathered all his uncontested rebounds (there may have been freak occurrences when a player missed one, but not to a statistically significant level). We then determined the difference between uncontested rebounds and rebound opportunities to come up with contested-rebound opportunities.

So if a player had 100 rebound opportunities and 50 uncontested rebounds in 10 games, 50 opportunities were contested.

The next part of our equation divided the number of contested rebounds by the number of contested opportunities. Therefore, if the same hypothetical player had 25 contested rebounds in his 50 contested opportunities, we would know he won half his rebound battles.

Next, we multiplied the percentage of rebounds won by the total rebound opportunities. So in our hypothetical situation, that's .5*100 (50). Over 10 games, that comes out to 5.0. 

That told us how many rebounds a player would have if all his opportunities were contested. We then adjusted for pace, and the result is Rebounder Rating.

The rebounder is rewarded for both his “winning percentage” of contested rebounds and getting himself into position to get them, thus factoring in both types of rebounds, but giving more credit for the contested ones.

The 95-Percent Test and Trends

The 95-percent test is the first thing I like to apply to a new metric. It should look mostly right but not exactly what I expect. If Jose Calderon is the leading rebounder, then there’s a problem with the metric. On the other hand, if it looks exactly like the traditional rankings, there’s no point to the exercise. It should look about "95 percent" correct. 

Here is how traditional rebound numbers compare with Rebounded Rating.

The correlation was strong enough to hold water, but not strong enough to render it useless.

There are some things that aren't exactly what you would expect, such as Kevin Love's distant-third ranking. However, once we dug into the numbers, it was understandable why. Fromal explains:

Love is a fantastic player on the boards, and only one player in the NBA produced more rebounding chances per game than the 18.9 he generated in his final season with the Minnesota Timberwolves.

He just doesn't convert them at a high enough rate (66.1 percent), and he thrives on uncontested rebounds. Only 38.9 percent of his conversions were contested, which is significantly fewer than the 40.3 and 45.8 percent boasted by the two remaining players in this countdown.

A new metric should also reveal trends. By identifying them, we can further our understanding of what happens on the court. It’s important to realize that in developing these metrics we aren't looking to “prove” something so much as learn something. We don't know what they'll reveal until we've done the math.

When eyeballing the numbers, it appeared that—for the elite rebounders—bulk mattered more than height. So I put the theory to the test.

I narrowed the field to players who had a Rebounder Rating of at least 6.0 per 36 minutes and played 20 minutes per game. That gave me a field of 36 players.

I then entered the height and weight for each player to see if there was any correlation with either factor.

In the following chart, I put height in feet and weight in 10s so the lines would be on a similar scale:

Original Excel Chart

After a certain point, it appears height means less and less. In fact, while there is a definite incline in the weight trend, it appears that height has a very slight decline.

Here is the same data in an infographic so you can mouse over and get the specifics for each player.

To further test the viability of my observation, I looked at the same data by groupings. I determined the average Rebounder Rating per 36 minutes by each height (in inches) and weight (every 10 pounds).

First, here’s Rebounding Rating by height: 

Below 6'10", it seems that height matters a lot. Almost all the elite rebounders are in that neighborhood. But once you get into that seven-foot range, it doesn't seem to matter at all. Admittedly, standing reach would be a better comparison than height, but since I don’t have the raw data for that, I had to settle for what I could get. 

Now, here it is by weight:

What is particularly striking here isn’t just that it goes up, rather how much it goes up by. Clearly, you need the height, but as the last column demonstrates, having 20 or 30 pounds when you're trying to get that extra board seems to matter more than an extra inch or two. 

It seems that bulk matters as much, if not more than length. Having the mass to body up, box out your opponent and grab those contested rebounds is a major factor.

This also establishes that a true gauge of rebounding abilities must factor in the difference between contested and uncontested rebounds. 

Nuggets

Ben Margot/Associated Press

The other fun part of something like this is finding the nuggets.

Here are some tidbits that include all players with five rebounding opportunities per game and 20 games played:

  • The two players who won the highest percent of their rebound battles were Kevin Durant (74.9) and LeBron James (74.0).
  • Jeremy Lin was the least likely player in the league to win a rebound battle, overcoming his opponent just 46.5 percent of the time. Ekpe Udoh of the Milwaukee Bucks was the second worst (46.7).
  • The two players who fought for the most rebounds per game were Andre Drummond (6.1) and DeAndre Jordan (5.5).
  • Jordan and LaMarcus Aldridge tied for the most uncontested rebounds per game (8.1). 
  • Ryan Anderson had to fight the hardest for his rebounds, grabbing .4 more contested than uncontested boards per game. Robin Lopez (.1) was the only other player to be above zero.
  • Aldridge was the least likely to have to contend for his boards, getting 5.1 more uncontested than contested ones. Al Jefferson (4.1) had the second-easiest time.

All of these next bullets are based on having a minimum Rebounder Rating of 6.0 per 36 minutes, the standard I set for elite rebounders:

  • Jordan is the best pound-for-pound rebounder, registering a .39 Rebounder Rating for every 10 pounds. Drummond is second at .38.
  • The most efficient player in inches per rebound is Drummond, who averages a .127 Rebounder Rating per inch. Jordan is second at .124. The pair pretty much have their own little rebounding planet, and no one else even has a spaceship to get there.
  • The shortest player to have a Rebounder Rating of 6.0 or higher is the Kenneth "Manimal" Faried, who is 6’8”. He is also the third-lightest player at 228 pounds.
  • Anthony Davis and John Henson are tied for the slightest elite rebounders. Both weigh only 220 pounds.
  • The Denver Nuggets, with Faried, J.J. Hickson and Timofey Mozgov, are the only team in the league with three elite rebounders.
  • Four teams, the Atlanta Hawks, Indiana Pacers, Miami Heat and Phoenix Suns do not have an elite rebounder.

Here is your NBA All-Rebounder Rating Team:

NBA All-Rebounder Rating Team
PositionPlayerTeamRebounder Rating
Point GuardRussell WestbrookOklahoma City Thunder3.03
Point GuardKyle LowryToronto Raptors1.81
Shooting GuardLance StephensonIndiana Pacers3.50
Shooting GuardJimmy ButlerChicago Bulls2.30
Small ForwardCarmelo AnthonyNew York Knicks5.22
Small ForwardLeBron JamesCleveland Cavaliers4.52
Power ForwardKevin LoveMinnesota Timberwolves7.80
Power ForwardTim DuncanSan Antonio Spurs6.12
CenterDeAndre JordanLos Angeles Clippers10.12
CenterAndre DrummondDetroit Pistons9.38
Original Research

Warts

Jim Mone/Associated Press

The biggest flaw we can identify here is that Rebounder Rating doesn't distinguish between offensive and defensive rebounds. While we’d love to be able to do that, it's not possible. The SportVU data doesn't separate them, so we can’t either.

That might not matter as much as you think. The consensus has been that defensive rebounds are easier to get because the team missing the shot is often getting back on defense. But that's not always the case (if it were, there would be no contested rebounds). Rebounder Rating actually accounts for that factor more accurately. 

However, it would be interesting to see if some teams and/or players are more likely to vie for shots on one end of the court than the other.

The second factor that we can’t account for is how teammates are involved. We don’t know if the other player contending for a rebound wears the same uniform or a different one. Teams with multiple elite rebounders could actually hurt one another’s numbers by scrapping for the same board.

By the same token, there are cases—such as with Kevin Love and the Minnesota Timberwolves—in which a player's teammates will just defer the rebound to him knowing he’ll get it anyway. In such cases, he gets credited for uncontested rebounds when he would have won the challenge regardless. That can actually have a slightly negative impact. 

If we could tell the difference between a conceded rebound (another player could challenge but chooses not to) and an uncontested rebound (in which no one could challenge, even if they wanted to), we could adjust for that. 

Other than that, we think we've done the best we can with what’s available, but we’re always looking for fresh input on how to improve. As with our Passer Rating, if you have some ideas for tweaks to improve the metric, feel free to let us know.

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