Friday, March 27, 2009

I May Not Get There With You

During last night’s Suns-Blazers tilt, TNT announcer Doug Collins described Suns guard Jason Richardson as a “volume shooter” who needs to take a lot of shots to be “effective”. This is a common locution in pro basketball analysis, but I’ve never fully understood what it means. Is this is a backhanded way of saying that a player like Richardson plays no defense, grabs no boards, and is not much of a passer – so his only contribution to the team would be by scoring? But then the effect in toto of having him on the floor, considering all his negative contributions, would not be very good. Or is it a way of saying that J-Rich is an insecure and quirky guy who needs to develop a “rhythm”, or perhaps feel that he will be getting a lot of shot opportunities that day, in order for his shots to go in?

To try to further unpack some of these notions, we here at JPO did some simple statistical analysis and uploaded our data to public Google Docs spreadsheets. We considered J-Rich’s stats for the current season with Phoenix (though the data is a bit abbreviated, as he has only played about 50 games with the team after being traded from Charlotte) and his 2007-08 stats with Charlotte, during which he played in all 82 games.

In both seasons, we calculated some simple correlations between various offensive performance metrics. Some of the correlations are obvious: if a guy scores more points or makes more buckets, then his team probably tends to score more points, and is more likely to win, so we expect a positive correlation. In evaluating the question of whether J-Rich’s taking more shots helps his team win, we focused in particular on the simple correlation between his FG ATT and his team’s win or loss outcome.

We found a weak 7% correlation in both seasons. Of course, causality is hard to interpret. This could mean that the team thrives when J-Rich shoulders relatively more of the scoring responsibility, freeing guys like Okafor or Steve Nash to do their thing. On the other hand (particularly with Phoenix) it could simply mean that the team thrives playing a faster pace, and more FG ATT by J-Rich is indicative of more FG ATT by all players on the team, and thus a higher chance of winning. These calculations would be easy, though we did not explore them due to lack of interest in gathering the data.

We also calculated the correlation between J-Rich’s field goal attempts and his field goal percentage in any given game. We found a 31% positive correlation with Charlotte, and a 17% positive correlation in his Phoenix tenure. So there is some evidence there that he is more accurate when he shoots more. On the other hand, this evidence could mean that his teammates are passing him the ball more because his initial shots on a given night were relatively accurate and they perceived he had a ‘hot hand’. Again, we could track this more precisely by gathering intra-game shot cart data and measuring accuracy over time within one game, but we really didn't feel like it.

We also computed J-Rich’s average FG attempts in wins and his average FG attempts in losses, and performed a two-tailed t-test based on a null hypothesis that the two averages are the same. Similarly, we computed J-Rich’s average points in wins and his average points in losses, and performed a two-tailed t-test for the null hypothesis that the two averages are equal. Basically, the difference was not significant at any reasonable level. Richardson’s points output shows a statistically significant difference (at a 10% level) in his teams’ wins vs. his teams’ losses, but we kind of expected that, as discussed above.

So in sum, I still have no idea what is meant by “he needs a lot of shots to be effective”. If he can’t do much other than score, why keep him on the roster? Someone more scrappy who can score less but do more other good stuff would be more valuable. J-Rich has by far the worst net plus-minus rating of any of Phoenix’s stars. Perhaps the secret of his “effectiveness” is more economic: fans come to see fireworks, not box-outs and extra passes.

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