Monday, November 11, 2013

Wins, Effective FG% and Defensive Rebounding

Two factors that I would expect to contribute to wins are FG% and defensive rebounding. The former signals efficient point scoring and the latter reflects an ability to end an opponent's possession. But it gets more complicated than that. Is it more important to be a really good shooting team that only takes two point shots but is awful at three point shots or is it better to be solid to mediocre at both twos and threes? Effective FG% (eFG%) takes three point shooting into account and, thus, values a team (or player) that goes 2-5 from 3FG as equal to that of a player that goes 3-5 from 2FG (both result in 6 points).

The problem with measuring actual defensive rebounds (or defensive rebounds per game) is that it belies teams that play abysmal defense and block few shots or fail to cause turnovers, or that control defensive rebounds so poorly that opponents get multiple FG attempts per possession. A multitude of defensive rebounds does not necessary reflect superior defensive rebounding; rather it could reflect disproportionate opportunities to secure defensive rebounds. Defensive Rebound Percentage (DRB%) takes this issue into account because it reflects the percentage of defensive rebounds that a team or player secured while on the floor of total defensive rebound opportunities. Thus, no matter how many or few defensive rebounding opportunities there were for a team, a higher percentage indicates that given the opportunities the team was successful at securing defensive rebounds and, thus, ending an opponent's possession.

I pulled team data from for the 2012-13 season and the 2013-14 season (through last night's games). For the 2012-13 season I collected data on total wins, eFG% and DRB%. For the 2013-14 season I collected the same information but used winning percentage in place of wins as not all teams have played the same number of games so far.

eFG% runs on the vertical axis and DRB% on the horizontal one. the circles in each chart increase with wins or winning percentage so a team with more wins receives a larger circle (and the Charlotte Bobcats, vice-versa). If eFG% and DRB% contribute to more wins then we would expect all of the large circled teams in the top right corner of the chart (signaling both high eFG% and DRB%) and all the small circled teams in the bottom left corner (signaling both low eFG% and DRB%).

Based on last season, most of the more successful teams, like the Heat, Spurs and Thunder all scored relatively high on eFG% but with the exception of the Spurs, Rockets and Warriors were relatively mediocre in terms of DRB%. (Note that the Charlotte Bobcats were worst at both.)

So far this season, it's kind of the opposite--the Spurs, Thunder and Pacers appear to be at the top or at least above average in terms of DRB%, and the teams with the highest eFG%, the Heat, Warriors and Clippers, are not atop the rankings. The fact that teams have played at most 7 games suggests that there is too small of a sample size to make any generalizations on 2013-14. Further, the Heat are again dominant in terms of eFG%, which over the course of a season will likely prove greatly beneficial for them, like it did last season. 

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