Shot Selection and Shot Making: A Quick Intro to XeFG%

Nov 25, 2014; Miami, FL, USA; Miami Heat center Chris Bosh (1) shoots over Golden State Warriors center Andrew Bogut (12) during the second half at American Airlines Arena. the Warriors won 114-97. Mandatory Credit: Steve Mitchell-USA TODAY Sports

Last week, I noted the detailed shot location and defense data available from SportVU via NBA.com allows for an estimate of “Expected” shooting percentages based on shot locations and strength of defensive contests. Along those lines, I derived XeFG for individual players as well as for team offense and defense. Through games of Tuesday, December 2:

As noted, this is all players with 41 or more shot attempts tracked by SportVU so far this season. XeFG% is what a player shooting at league average rates on the player’s mix of close, mid-range and three-point attempts would expect to shoot based on the defense attention those shots received. eFG% represents the observed effective field goal percentage on those shots and DEFG is the amount a player is either exceeding or falling short of his “expected” shooting percentage. At this point, there isn’t a systematic way for determining the degree to which this differential represents skill, short term variance and luck, or a player getting shots that are systematically easier or harder than general shots from various locations.

As a further bit of analysis, players with sufficient shot attempts both this year and last can be compared to see the degree to which their changes in shooting are as a result of the different shots they are taking or improved shotmaking:

One possible trend which is immediately visible is the degree to which players from last year’s Heat team are being forced into tougher mixes of shots — among the 25 players with the biggest increases in shot difficulty, 4 of them are from that squad:

Bosh’s place at the head of that list is wholly unsurprising giving his enormous jump in usage following James’ exit. Andre Drummond’s rough start to the season is visible as well, as though his shot quality has declined markedly in its own right, his wholly unpolished post game perhaps has rendered him particularly susceptible to reduced effectiveness from trying to create shots for himself.

Check “our stats” for regular updates of these and other metrics.