Robin Lopez and Rebound Value

By some estimation, the Knicks have had a disappointing start to free agency. They whiffed on most of the big names,[1. Assuming DeAndre Jordan is in fact deciding between just the Clippers and the Mavs] only landing role-player types Arron Afflalo and Robin Lopez. Lopez in particular has raised eyebrows, getting $54 million over 4 years for a center who is best described as “workmanlike.” It sure seems like a lot of money for a guy who averaged 9.6 points and only 6.7 rebounds last season.

Of course, the topline numbers aren’t all there are to Lopez. He’s been a good-to-very-good rim protector over the two years for which we have data. He’s an efficient scorer largely because he knows his limitations. Especially for a big man, he’s an excellent foul shooter, 77% or above for each of the last three years. Still, for the Knicks those numbers are vaguely underwhelming for a team which needs everything. Is 6.7 rebounds per game really going to cut it for a team that was 26th in defensive rebound rate last season?

It’s actually a trick question. A rebound is not always a rebound. As noted earlier this season, the available SportVU data can help us differentiate rebounds by type. A quick first pass indicates “uncontested[2. Per the SportVU definition of contesting a rebound is being within 3.5 feet, basically arms’s length, of the ball when the rebound is secured.]” defensive rebounds are “worth” about half as much as other rebounds. In many cases, these are the rebounds where by virtue of the fact that more defensive players than offensive ones are involved in chasing rebounds, the ball is going to bounce to a spot with no offensive player nearby quite frequently. In fact, roughly 57% of all rebounds last season were just this sort of “free” defensive rebound. A player looking to stat pad could get rich simply by gobbling these up at a high rate, perhaps even taking them away from teammates.

The general effect of what might be called rebound stealing (perjoratively) or simply diminishing returns to individual rebounding (more neutrally) has been discernable for much longer than we’ve had SportVU data. But this newer data does allow us to see just who is grabbing more or less than their share of these “free” rebounds. Again mirroring findings by Phil Birnbaum in the above-linked post, rebounding by big man seems to be more impactful than from the wings[2. This is just in terms of a simple question of grabbing more or fewer rebounds, some studies have suggested that rebounds by point guards in particular lead to better ensuing offensive possessions, but that’s another discussion for perhaps another day.] While the overall NBA rate is 57% of rebounds are free defensive boards, among rotation bigs, that number is closer to 52%. In other words just over half of their rebounds are those that someone on their team would probably have ended up with, whereas the other half have been actually fought over.

Which leads us back to Robin Lopez. Among the set of 100 or so regular rotation bigs in the NBA last year, the lowest proportion of Lopez’s rebounds  were these uncontested defensive types. Conversely his now ex-teammate LaMarcus Aldridge was among the leaders in

highest

proportion of uncontested defensive rebounds[1. The full list of rotation bigs playing 40 games with 15 minutes per game and at least 8 rebounds per 36 is below

]:

This isn’t to suggest there was any sort of skullduggery going on in Portland. It could just as easily be that Lopez’s job was more to prevent his assignment (usually the opposition’s best offensive rebounder) from getting to the ball, which allowed Aldridge to use his greater mobility to track the ball down.[3. There was probably a little bit of a star system going on since “double-doubles” are still a thing and averaging ten boards a game probably had value to Aldridge over and above it’s value to the team’s success. There are far worse ways for a player to be “selfish” so long as it isn’t so blatant as to cause a rift within the team.] That’s a sensible division of labor. But it does have the effect of making Lopez look like a “worse” rebounder than he probably is, when in actuality he was the guy most often sticking his nose in for the tough rebounds.

Whoever the Knicks run out next to him at power forward this coming year, he won’t have the same voracious appetites as Aldridge. While this puts more of an onus on Lopez to actually collect more of these rebounds, there is very little reason to suspect he won’t be able to expand into that void. Perhaps more importantly, Lopez’s willingness to battle will be vital to a team who gave up the 2nd highest[4. To Minnesota. hi Karl-Anthony!] rate uncontested offensive rebounds off of opponents’ misses last season, with 9.5% of all forced misses being recovered by the offense with no Knick nearby.[4. The Spurs, being the bastion of proper fundamentals they are, allowed the lowest proportion of uncontested offensive rebounds, at only 6.7%.]

While the mop-headed, mascot-hating Lopez might not be the big name supporters were hoping for, he provides exactly the sort of solidity both on the boards and defensively needed for a foundation. While the team has more work to do to add the “exciting” bits to the team, Lopez is emblematic of this offseason being a good start to a gradual and considered building process.