Usage is a term typically associated with offense. It’s an estimate of how often a player “uses” an offensive possession (the standard formula involves true shot attempts and turnovers). But we can think of usage in terms of defense too. That is, how often a player has a shot attempt taken by someone he is in the act of guarding.
According to my tracking, in the 2010 NBA Playoffs, 56.3% of true shot attempts (FGA’s + 0.44 * FT’s) were taken while being guarded. 14.0% of possessions ended in turnovers. The other 29.7% were either:
- open shots (as a result of a defensive breakdown, defenders being effectively screened out or from transition opportunities)
- free throws (from non-shooting fouls — the penalty — intentional fouls and technical fouls)
As expected, PG’s foul in the act of shooting less, they face fewer shots when guarding, and as a result fewer TS attempts. It scales up the “bigger” the position, with bigs facing more than half of the shots despite occupying only two of the five positions on the court. This is primarily because they play close to the basket and engage all of the players driving down the lane while protecting the basket.
In America’s favorite visual form, the pie chart, it looks like this:
This means that the range of defensive impacts will be much wider for interior players than perimeter plays. The difference between a good and bad defensive point guard won’t be nearly as pronounced as the difference between a good and bad defensive center. Using a simple mathematical example, imagine the following:
- A “Bad” Defender allows 50% eFG shooting
- A “Good” Defender allows 40%e FG shooting
Assume free throw accuracy is a constant (the league average). Based on these shooting percentages, at the center position the difference between our bad defender and good defender is 2.9 pts/100 (a difference in efficiency this year between an average team and the 8th-best team). But at PG, the difference between our good and bad defenders shrinks to 1.2 pts/100.
But that’s just looking at shooting. If we want to create a “Defensive Usage” stat to mirror the offensive one, we need to incorporate turnovers as well. When we do that, we end up with the following positional breakdown:
Practically speaking, individual defenders can have a slightly larger influence than presented above, as this methodology ignores factors like deterring a shot in the first place, defending the 3-point line and disrupting penetration on pick and rolls (incredibly valuable in today’s game). Those tasks fall primarily on the shoulders of little guys, so it’s possible for them to make up some of the difference in “usage” there. Nonetheless, it should seem quite intuitive that the giant men who protect the basket face the most shots — and the most high-efficiency shots — in a position to grab the most rebounds, and thus have the largest impact on the defensive end.
One last point to note is that all of this explains why great individual defensive players can’t have the same impact great individual offensive players can have. This should also be intuitive, as on offense, teams can choose to run the majority of plays through one player. On defense, they can’t choose to have the other team always attack their best defender; Great defenders are essentially saddled by guarding their own man or helping on a slasher down the lane. But as you can see, even that doesn’t involve them on nearly as many possessions as is possible on offense.
We can compare our new Defensive Usage stat with the traditional offensive Usage stat. Here are the leaders from last year’s playoffs:
Offensive Usage (min 300 possessions)
- Durant – 34.0%
- Wade – 34.0%
- Bryant – 33.2%
- Anthony – 32.1%
- Rose – 31.5%
Defensive Usage (min 300 possesions)
- Gortat – 23.7%
- Perkins – 21.6%
- Frye – 20.9%
- T. Allen – 19.4%
- McDyess – 19.4%
In reality, the difference is even greater than seen here because of the number of plays in which an offensive player creates for others yet the result isn’t attributed to usage totals. Although that’s the topic of a future post.