ESPN introduced a new advanced statistic on Monday called "NBA Real Plus-Minus." Like any individual statistic in a team sport, it is somewhat misleading. It can tell us interesting things about what a player is doing when they are on the floor, but it doesn't completely capture the value a player is (or isn't) bringing to his team. Jae "The Beast" Crowder is a textbook example of why that is the case -- he has an RPM of 2.53, which puts him at No. 9 in the NBA at the small forward position.
Player's estimated on-court impact on team performance, measured in net point differential per 100 offensive and defensive possessions. RPM takes into account teammates, opponents, coaches and additional factors
Here's why that is impossible. Jae Crowder is used primarily in a specific role in a certain line-up -- he's the small forward when Carlisle makes his second rotation of the half. Carlisle takes Dirk out early and goes with a small-ball team with Shawn Marion at the four, than he brings Dirk back in with Crowder, Brandan Wright and Devin Harris. That unit absolutely kills opposing second teams and Jae has very little to do with it.
All the Mavs are asking him to do is pass the ball, don't turn it over and be passable at defense. They run pick-and-rolls with Dirk or Wright and Jae is one of the guys who rotates the ball off the pick-and-roll. He's a league-average shooter who doesn't take many shots. The ones he takes generally tend to be open and he scores 10 points on 44% shooting per-36 minutes. There's just not much going on with the guy.
Jae is literally out there to give Shawn Marion a breather. Marion plays 31 minutes, splitting those between the three and four. The minutes Marion doesn't play at the three, Carlisle splits between Crowder and Vince Carter. Crowder will get spot minutes in a blow-out or when Marion can't go, but playing at the three when Dirk and Wright are in the game is the only defined role he has on this team.
Anything that measures the output of the possessions that Jae Crowder is on the floor is only measuring how well the Mavericks are doing as a team in that one role. He spots up and shoots threes at a league average rate and he is a decent defender at the wing position. The Mavs can't give the line-up he is in more minutes because a team that played Wright and Dirk together for more than 15+ minutes would not have enough rebounding or interior defense.
The only reason Dallas can get away with using that line-up -- the one that makes Crowder an effective player -- is because Carlisle uses it for four to five minute stretches against second units. He's putting Dirk and Wright, two of the most efficient offensive players in the NBA, against what are usually straight up terrible defenders. Backup fours and fives have pretty much zero chance of guarding Dirk or Wright. Just as important, they can't exploit their "defense" at those positions.
What this is really showing you is why Carlisle is such a good coach. He doesn't do rotations in broad strokes -- he has very distinct combinations of players he uses for very small periods of time for very specific reasons. If he staggered the minutes so that Jae had to play a ton with Samuel Dalembert or DeJuan Blair, it would be disastrous. That's just way too many liabilities to have on the floor at the same time.
What Carlisle is really doing is staggering Dirk and Marion's playing time in order to allow less effective guys to sponge off them. When Dirk comes out early in the first and third quarters, Carlisle brings in Vince and moves Marion to the 4, where he has to match up with starting power forwards. Not many NBA small forwards can hold up for any amount of time against Blake Griffin, Kevin Love, LaMarcus Aldridge and all the other great power forwards in the Western Conference.
Marion is doing heroic work. He gives up points to those guys, because who doesn't. The important part is that he is not being destroyed on the defensive end. His RPM of -0.67 is so much more important than Crowder's RPM of 2.53 it's not even funny. If you're a Dallas player being measured by your effectiveness, you want as many minutes with Dirk as possible. Marion plays a lot fewer minutes with his starting power forward than most starting small forwards, and Dirk is his starting PF.
The RPM statistic is measuring something real, but it's measuring the line-up choices of the Mavs coach as well as the strengths and weaknesses of the player Crowder backs up and the guys he shares the floor with. It only tells so much about Jae Crowder the player because his production is a statistical construct of Carlisle's ability to deploy personnel. There are a lot of guys who could do what The Beast does who are in the D-League -- because he doesn't do anything.
You could plug in any NBDL small forward and ask him to move the ball and play passable defense against second-unit wing players. It's a role that needs to be filled in order for the team to be successful, but it's a role that almost any professional basketball player, whether they are in the NBA, D-League or Europe, can fill. There's nothing you need to measure with Jae Crowder -- you just need to know the role he has on his team.
That's why Crowder is the textbook example of the problems with RPM. Marion, in contrast, has 3-4 different roles, which vary with the units he is on. He backs up Dirk and he plays with Dirk -- those are very different roles. The per-100 possessions production of any player is only a measure of the different roles they play on their team's various line-ups. There's no way to isolate that number because it's a product of how they interact with specific teammates.
Any number that punishes Marion for the production he gives as a backup 4 is missing the point. If you asked Crowder to play minutes as the back-up 4, it would not be a good situation. There's a reason The Beast is the only small forward with an RPM of more than two to play less than 20 minutes a night. If you want to know how good he is as a player, all you have to do is look at what his role is for the Mavericks. Anything else just confuses the subject.