Fun With SportVU: Successful Assist Percentage


Every day, the SportVU player tracking data becomes more and more robust, which gives nerds like me more numbers to play with. While we might only have a limited subset of all of the data that the tracking cameras gather, there’s still plenty to pore over and manipulate.

Much of the focus thus far has been on passing statistics; on Tuesday night, the Dallas Mavericks broadcast referenced the secondary (or “hockey”) assist numbers available on NBA.com. Of particular interest to me is the ability to see how many assist opportunities (defined as “passes by a player to a teammate in which the teammate attempts a shot and, if made, would be an assist”) a player has relative to the number of actual assists he registers over the course of a game. In that vein, I took a look at the top 25 players in assist opportunities (minimum 5 games played/20 minutes per game) and their “successful assist percentage,” an easily derived metric that measures how many potential assists a player’s teammates actually convert.

Data accurate through the games of 11/11/13.


Even such a simple exercise can provide a fair amount of insight into the games that we previously could only guess at. Perhaps foremost among those conclusions is the realization that, at least in the early going of this season, even the best passers with the best shooters around them only convert a shade under 60% of their assist opportunities.

On the other end of the spectrum, it’s interesting that Grevis Vasquez and Isaiah Thomas, both Kings, have had their teammates knock down the shot after a pass so infrequently. The data there points to the fact that Sacramento simply can’t shoot the ball this season; they’re a bottom five team in effective field goal percentage. The Chicago Bulls and Utah Jazz are also among the cellar dwellers in eFG%, backing up the low successful assist percentage for Derrick Rose and Gordon Hayward, respectively. It’s somewhat surprising that Kevin Durant’s passes would so often fail to produce an assist, at least on the surface. But given further consideration, it certainly makes at least some modicum of sense: the Thunder have yet to shoot the ball well (they’re a bottom-10 eFG% team), and a fair number of the shots that do fall for Oklahoma City naturally come from Durant.

Messing with the data like this is a fun exercise from which we can glean certain facts, but the real conclusion here is that no matter how much information we gather, analysis of the numbers will always be a science and an art. Plugging the statistics into a spreadsheet and doing simple division can reveal certain trends, but those trends deserve and necessitate context. As I’ve written before, the revelations produced by SportVU aren’t answers, but further questions. To whom is Ty Lawson passing, and why are they unable to knock down the shots he creates for them? Is it a matter of decision-making, with Lawson simply not finding the right players in the right spot, or is he without other options? With such a small sample size, is the issue for some players — on both ends of the spectrum — simply a matter of a bounce or two going for or against them? And when a player like Durant has the ball in his hands, what’s the marginal expected value of his taking the shot versus passing the ball to someone whose chances of making a basket might be significantly lower?

We stand on the tip of the iceberg, trying to drill to its core. For now, we’re stuck with hammers and chisels, but at least it’s a start.

Statistical support courtesy of NBA.com/stats

Andrew Lynch

When God Shammgod created the basketball universe, Andrew Lynch was there. His belief in the superiority of advanced statistics and the eventual triumph of expected value-based analytics stems from the fact that he’s roughly as old as the concept of counting. With that said, he still loves the beauty of basketball played at the highest level — it reminds him of the splendor of the first Olympics — and the stories that spring forth from the games, since he once beat Homer in a game of rock-paper-scissors over a cup of hemlock. Dude’s old.