Defensive Rebounding Has Become the Most Undervalued Defensive Skill in the NBA
Judging defensive value for NBA players has come a long way over the last several years, but we’ve still zigged and zagged quite a bit recently. The "best" defensive players used to be whoever we thought was the “toughest”. Then we started valuing players who could rack up blocks because it was all about protecting the rim. Then we realized that rim protection and blocking shots don’t go hand in hand (if we hadn’t learned about this, DeAndre Jordan would have been Defensive Player of the Year this year).
We used to really value defensive rebounding –- after all, the point of defense is to end a possession without the other team scoring. You can protect the rim all day and block a million shots, but if you never grab the defensive rebound, you’re defeating the purpose of defense. But that’s not quite as sexy to us basketball watchers anymore, and it hurts our basketball eyes when we see a player who looks like a defensive negative have positive defensive metrics.
Cavaliers forward Kevin Love is a clear example of this. Most basketball analysts watch him play and see a subpar defensive big. And, gasp, to basketball analysts, there isn’t anything worse than a defensive big in 2015! However, look up Love's Defensive Real Plus-Minus (plus-1.46), Defensive Rating (105), on-off court numbers -- or any other statistic -- and you will find a positive defensive player. So what gives?
Defensive Stat Correlations With Defensive Metrics
My theory is that we’re now undervaluing defensive rebounding as a valuable defensive skill. There are two ways a possession can end -– a defensive rebound or a turnover (be it a travel, steal, or whatever). The former happens much more frequently than the latter, however, and a player who can end possessions at a high rate is valuable in their own way.
To get some data on this, I looked at players this year (500 minute minimum) and how three stats (defensive rebounding percentage, steal percentage, and block percentage) correlated with two defensive metrics (Defensive Real Plus-Minus and Defensive Rating). Let’s start with all players (guards, wings, and bigs) and then we’ll sort to just bigs.
On an NBA level, it seems that defensive rebounding actually has a higher correlation with DRPM than both block and steal percentage. Interestingly, there was essentially no correlation with any of the three stats with Defensive Rating. I’m not really sure why this is -– perhaps because Defensive Rating is much more affected by teammates, as opposed to DRPM which attempts to adjust for that?
As said above, blocking shots doesn’t always mean the rim is being protected, so this data isn’t telling us that Kevin Love is a more valuable defensive player than Rudy Gobert or anything. The point isn’t that blocking shots and rim protection isn’t important; it’s that defensive rebounding is also important.
Big Man Defense
To make sure the data isn’t skewed by the guards, let’s look now at just data for the bigs.
This is interesting -– the correlation actually drops for bigs, although it’s still much higher for both defensive rebounding and block percentage than it is for steals. I’ve been thinking about why this could be, but don’t have a great answer right now. It could have to do with how DRPM is calculated –- perhaps it adjusts for big men? It seems like this might be true, as the very top of the DRPM charts are all big men.
I wonder what a perfect big man combination would be -– one player that can protect the rim at an elite level and one player that can defensive rebound at an elite level? If the Pelicans re-sign Omer Asik, they’ll be a good case study of this, as Anthony Davis will be an elite rim protector soon enough and Asik is one of the best defensive rebounders. It seems like a great combination on paper, but the returns this year weren’t as expected.
We still don’t have perfect defensive metrics, though things are getting better. SportVU cameras and resulting rim protection statistics, like from Nylon Calculus, will continue to illuminate how to value defenders. Rim protection is the trendy subject right now, but don’t be surprised if we come back around on elite defensive rebounders as very useful defensive players.