There are a few ways offenses end up with unguarded shots, either in transition, off of screens and when defenses make errors. The thinking here is (deliberately) quite simple: defenders should be guarding someone. If they aren’t, they should be rotating or hedging a screen to resume guarding someone. The goal is to not give up open shots, which is always trumped by the goal to not give up open layups.
I categorize defensive errors in two ways:
- A blow-by
- A missed rotation
The first is an error in man defense, when one’s man beats them to the rim – “blows by them,” in hoops vernacular – either with the ball or off the ball. It’s a “blow-by” when the defender is no longer engaged in guarding the player. The second is an error in team defense, when players fail to logically rotate to an open defender, or even worse, don’t rotate to the rim to prevent an open layup (the majority of “missed rotations”).
In either case, two players can receive half an error each if two players were equally involved in the error. For a blow-by, this is simply when a double-team is split and left in the dust, but for a missed rotation it is equally blaming two proximal defenders who could have rotated to an open man and did not. It’s common for half missed rotations to take place when two players incorrectly rotate to the same shooter on the perimeter and fail to collectively protect the rim against an open layup. (They usually then start pointing at each other or looking around in befuddlement. The lesson: defensive communication is important!)
Defensive errors essentially create a power play — similar to the power play we saw in opportunities created — that spikes the opponent’s offensive efficiency by nearly 50%. In the simplest terms, tracking defensive errors is assigning responsibility to players who give up open shots when they otherwise shouldn’t.
As is the case with assigning credit for an assist, there is a gray area (mostly involving whether a player could have rotated and didn’t).
Some examples of defensive errors:
- Being beaten off the dribble and no longer being within reach of the dribbler (BB)
- Being backdoor cut on the wing without staying with the cutter (BB)
- Being run by on the way down the court by your man (BB)
- Failing to rotate to the basket when the screener rolls free as his defender double-teams the dribbler (MR)
- Failing to rotate to a man to box out after a similar defensive scramble (MR)
- Staying in the backcourt (cherry-picking) and not running back in a reasonable time to defend anyone (MR)
Through March 15 (162 team games tracked), here are the players with the most defensive errors in the 2011 regular season (minimum 300 possessions played):
And the players with the fewest defensive errors:
*Qualifier players for leaders listed in this post play for: Atlanta, Boston, Chicago, Dallas, Denver, Indiani, LA Clippers, LA Lakers, Miami, New Orleans, New York, Oklahoma City, Orlando, Phoenix, Portland, San Antonio, Utah. Remaining teams don’t have 300+ possessions in the 2011 database.
For those wondering, the correlation coefficient between defensive errors and team defensive rating this year is about 0.35.