By: Richard Li
While watching games, I'm simultaneously intrigued by and skeptical of the stats that announce that player X does activity Y at Z effectiveness when his team wins, and does so much less when his team loses. It's a nice thought, that one player's specific behavior might indicate, or even predict, his entire team's outcome. To make this activity a little more robust and interesting, I decided to inject some statistical steroids into the traditional analysis. Below is a graph that shows the difference in five indicators (assist ratio, defensive rating, offensive rating, true shooting percentage, and usage percentage) between team wins and losses of all nine of the Houston Rockets regular rotational players (click for a full-sized interactive version).
First, the boring technical explanation. Offensive and defensive ratings are points per 100 possessions. Assist ratio is the number of assists and individual player has per 100 possessions. True shooting percentage is a field goal rate that considers three-point shooting percentage and free throw percentage. Usage rate is an indication of how much of a team's percentage is "used" by a certain player (i.e., how many times a player shoots, goes to the line, etc.).
On the x-axis are players, excluding Asik due to lack of sample size. Leading each cluster of players is the Houston Rockets as a whole (the red bar). Also on the x-axis are the players' performance in five statistical categories. The y-axis shows the players' percentage difference in those five aforementioned categories in games that the team wins and games that the team loses (1 -(statistic in wins/statistic in losses)). Please note this is the percentage change in the statistic, not the nominal change, and is always the difference from team wins to team losses.
A positive percent change indicates that the player is "higher" in that statistic in games in which the team loses . A negative percent change indicates the opposite. Keep in mind that for defensive and offensive points per 100 possessions, a positive percent change means more points in losses than wins. Looking at the graph, this means the Houston Rockets give up more points and score less in losses than wins, no surprise there.
Onto some quick hitting observations.
- Francisco Garcia appears to be the most offensively volatile but defensively consistent player. The difference in his offensive rating and TS%, especially his TS%, is the greatest on the team, while the difference in his defensive rating is the smallest.
- The point guards actually have more assists per possession in losses than in wins.
- The team's "stars" and Casspi (?) see an uptick in usage during the team's losses.
- The previous two bullet points might indicate that the team defers more to certain players in losses than in wins.
Finally, a warning about how to interpret these results. These data DO NOT show causality. In fact, the directionality of these data is completely unknown. Basically, we don't know if the Houston Rockets start losing once Dwight Howard is featured more, or if Dwight Howard is featured more once the Houston Rockets start losing. Either scenario is equally plausible for each indicator. Also possible is that a player's performance in a statistic has no relationship at all to the team's winning and losing. For example, take Francisco Garcia's defense, which changes the least from team wins to losses. It could mean that he is a tenacious and persistent defender whose energy does not decrease when the team is losing. Or it could mean that what he does defensively doesn't really affect the outcome of the game.
