The Wages of Wins folks had a discussion on usage recently, and in the meantime I’ve had some thoughts percolating on if there should really be a usage-efficiency tradeoff or not. This isn’t meant to be an all-encompassing treatise on usage (although I considered it), but hopefully more of a few notes and a demonstration.
First, let’s start with the definition. Usage is an estimate of how many possessions (usually scaled out of 100, so it can be a percentage) a player uses while he’s on the court. Players can use a possession by taking a shot (which includes some percentage of free throws) or turning the ball over. Taking a shot doesn’t always use a possession because someone could get an offensive rebound, but as far as basketball-reference is concerned, player usage is turnovers plus ‘true’ shot attempts.
Next, let’s talk theory. Hypothetically, there must be a usage-efficiency tradeoff due simply to game theory. Let’s say that I knew (or quickly caught on during the game) that LeBron was going to shoot the ball every time; he was not going to pass and he was always going to get the ball. The defense would quickly key in and he would face all five defenders, none of which were worried about him passing and potentially messing up his 100% usage rate. His efficiency would be lower than if he were willing to pass here and there. At the other end, let’s say that Tyson Chandler is never allowed to touch the ball unless he’s wide open at the rim for a dunk. Because he rarely has the ball, and in fact may even be convinced by teammates to not look directly at it, Chandler will have a very low usage rate. But when he does get the ball he will be a very efficient scorer because all he has to do is dunk the ball before someone swipes it or fouls him. These two endpoints define a spectrum that seems to point pretty directly at a tradeoff existing.
So if this theoretical discussion is so convincing, why do I not particularly believe in the tradeoff (as can be seen here, for example)? The main reason is because players play against actual opponents, and so game theory has already restricted the kind of usage rates we see. For guys who played at least 10 minutes per game for at least 5 games last year, usage fell somewhere between 35.7% (Kobe) and 5.1% (Andris Biedrins). These are presumably pretty representative numbers for the range of usages that will actually occur in a reasonable sample of NBA games. So for all practical purposes, the question isn’t if a usage-efficiency tradeoff exists, it’s does the tradeoff exist in this range. After all, NBA decision makers have to use information that applies to the game their players play, not the game that happens in thought experiments.
Now I’m going to change gears a little bit. Instead of trying to prove whether the tradeoff exists or not (and you can find links to people who have tried in the WoW link above), I’m going to try to demonstrate that changing your usage up or down should be very easy. If changing your usage is very easy, I think it follows that any potential effects on efficiency should be pretty minor. But we’ll see how it goes.
For my example, I’ll pick on Kobe because he makes it so easy to do so. Let’s start with the Lakers as a team. Last year they had an average pace of 90.5, which means that per 48 minutes they would be expected to use 90.5 possessions. Team possessions includes an adjustment for offensive rebounds that doesn’t happen at the player level for usage, but that’s ok. The main point is, we can expect the Lakers to have a combination of shots, free throws, and turnovers that add up to the neighborhood of 90.5 per game. Now if we look at Kobe, we see he took 23 shots per game, another 7.8 free throws, and turned the ball over 3.5 times. That means Kobe used 29.9 possessions per game (roughly speaking; bball-reference doesn’t list the exact formula for player usage). Knowing that Kobe uses about 30 of the Lakers’ 90 possessions tells us that Kobe should have a usage of around 33%, which is close to the actual number of 35.7%. Getting it spot-on isn’t the point, so much as demonstrating that we can use team pace and player shots+FTA+TOV to get a decent estimate.
So let’s say we can convince Kobe to take one fewer shot per game by passing it to someone else or just taking a play off, so to speak (not by turning the ball over). He would use 29 out of 90 possessions, and his usage would be around 32%. In general, since usage is scaled out of 100 possessions and there are around 90 possessions in an NBA game these days, shifting a possession per game from one player to another should move their usage by about a percent. Kobe could have moved his career-high usage of last season to his (still high) usage in the 2009 championship season by taking three fewer shots per game. He could also just let someone else handle the ball more, since lowering his turnovers would also lower his usage.
Shifting possessions around shouldn’t take a giant effort. Big men can flash through the paint or roll harder after a pick a couple extra times per game. Shooters can have an extra screen play or two called for them. The point guard could just pass to a different guy here or there. It wouldn’t take a change in offensive philosophy, just a tiny bit of an effort. If that sounds reasonable, then you could have fairly dramatic changes in usage. We tend to talk about the outliers, like Kobe or Biedrins, but a lineup of five average guys would put each player at 20%. If it doesn’t take much effort to shift usage by, say, 2 or 3% in either direction you could take a guy like Pau Gasol (22.1% last year, 98th in the league) and make him Corey Brewer (20%, 161st); you could take Brewer and make him Marvin Williams (18%, 220th). A couple plays a game, the tiniest change in emphasis, and usage shifts across 80 players.
So changing usage should be pretty easy. What would it do to efficiency? Obviously that’s the tougher question. If Kobe could be bothered to give up some of his 7.7 long jumpers per game his efficiency would definitely increase (although Kobe has a remarkably flat eFG% across shot distance). If he tries to avoid a bad shot but throws a bad pass instead, his efficiency would actually go up a little (his usage would stay the same, but his shooting accuracy would increase). But if he gave up the opportunities he got at the rim, his efficiency would go down. Similarly, if a guy gets stuck with the ball as the shot clock runs down an extra time or two per game, his usage will go up and his efficiency likely down. In short, there’s no easy way to predict which way efficiency ‘should’ go. If a team just tried to get a guy his preferred shot (the one he’s good at, not necessarily the one he likes taking) an extra time per game, usage and efficiency could go up together. If a team just dumped him the ball and said “bail us out”, his usage and efficiency would head in opposite directions.
That, in a nutshell, is why I think the necessity of a usage-efficiency tradeoff is overblown. Changing usage is easy. What happens when usage changes is not. Efficiency definitely does not need to decrease just because a guy has the ball more; the guy could be getting more shots that he’s good at. A guy who gets the ball less could have his efficiency go down because he gets antsy and starts jacking up shots when he does get an opportunity. If someone like Kobe wants to increase his usage, he will probably see a decrease in efficiency because he already uses so many that eking out another probably has to happen in a less-than-optimal situation. But anyone in a more reasonable range should have a fairly easy time. Does anyone doubt that Pau Gasol couldn’t get the ball one or two more times without suffering? What if Jeremy Lin didn’t have to just hand the ball to Carmelo, but could run a play and get a shot (Lin was 21st in usage last year, at 28.1%)? It could go the other way; it’s easy to envision Amare Stoudemire’s role decreasing while he simultaneously relies more on jumpers, lowering both usage and efficiency. Could Monta Ellis get less of the green light in Milwaukee but take even more long jumpers? These all seem plausible, if not likely, and go counter to a tradeoff.
So in general I don’t take a tradeoff for granted. I won’t go so far as to say it absolutely doesn’t exist, because again in some situations it must. But I solidly believe that the conditions are so variable that any effects are going to be very noisy at best.