Deron Williams may have been the third-best player with the ball in his hands last season, according to a new metric devised with the NBA’s new optical tracking data. But how real are the numbers?
The metric, devised by Dan Cervone, Alexander D’Amour, Luke Bornn, and Kirk Goldsberry called “expected possession value added” (or EPVA), attempts to assess how much a player positively impacts a possession with a monumental amount of data. (Read the research paper here.) In short, it uses the league’s optical tracking cameras to estimate the value of a possession in certain places, and how much a certain player’s movement with the ball impacts the value of possessions over the course of a game.
Basically, it seeks to answer this question: how much did a player, while holding the ball, impact his team’s chances of scoring?
An example used by Kirk Goldsberry in his Grantland piece on the research:
(I)magine LeBron James holding the basketball completely unguarded underneath the basket. We would expect him to score two points. The EPV at that moment would be very close to two. Conversely, imagine Dwight Howard holding the ball 40 feet from the hoop with one second remaining on the shot clock and three defenders in his face. It’s highly unlikely that Howard would score. That moment would be ascribed an EPV very close to zero.
According to the metric, Brooklyn’s Williams added 2.52 points per game above a replacement-level player, behind only Dirk Nowitzki (2.60) and Chris Paul (far and away the leader, with 3.48) among players who played at least 100 possessions.
There are significant limitations within the data, though. For one, only 13 arenas had the SportVU cameras installed last year, and Barclays Center wasn’t one of them. While that might actually be a point in his favor — Williams looked good by the numbers even on the road — it allows for some wonkiness in sample size. The paper acknowledges that restriction, and with all 30 teams installing the cameras for this season, there will be much more data to look at.
The “smell test” comes back with mixed results. Williams is surrounded in the top 4 by bonafide All-Stars Chris Paul, Dirk Nowitzki, and Stephen Curry, and other members of the top 10 include LaMarcus Aldridge, Steve Nash, and Damian Lillard. Jamal Crawford, who never met a ridiculous move he didn’t like, is the only questionable player on the list. That said, neither LeBron James (ranked 23rd) nor Kevin Durant made the top 10, and the bottom 10 is filled with All-Stars: Kevin Love, Paul George, Russell Westbrook, Jrue Holiday, and Roy Hibbert all rank poorly.
Williams has struggled this season with injuries and consistency, admitting recently that his confidence hasn’t been particularly high, but performed strongly in the last three quarters of Thursday night’s game. “I think Deron’s energy level’s high,” coach Jason Kidd said after the game. “He’s starting to get his legs underneath him.”