Reinterpreting “Defenders” with SportVU

Jan 2, 2015; Salt Lake City, UT, USA; Atlanta Hawks forward Paul Millsap (4) tries to block the shot of Utah Jazz forward Derrick Favors (15) during the third quarter at EnergySolutions Arena. Atlanta Hawks won the game 98-92. Mandatory Credit: Chris Nicoll-USA TODAY Sports

Paul Millsap deserves a recount.

With the flood of new NBA analysis thanks to NBA.com’s SportVU data, discussion of players’ ability to alter shots has been saturating the Internet datasphere. Including myself, people have been quoting metrics which assign defensive credit to whichever player SportVU’s cameras find to be the “closest defender.” The problem is, there are many cases in which the closest defender is not the primary shot-alterer. I can prove this with one simple number from this season’s data:

On 31% of all blocked shots, the “closest defender” is listed as a different player than the blocker.

Why does this happen? As you might expect, shot attempts close to the basket are often met by bigger clumps of players (help defense is a good example). Misappropriated “closest defender” shots this season have happened with the median “closest defender distance” of just 2 feet, and a median shot distance of 4.9 feet from the basket. The closest defender could be anywhere in that 2-foot radius!

Which brings us to Paul Millsap — whose blocks are being “closely defended” by different players at a higher rate than anyone else with at least an average number of blocks.

A variety of Hawks are associated with this phenomenon, most frequently Kyle Korver. On nine of Millsap’s blocks Korver is listed as the closest defender. Biggest number of blocks made when another player is closest? Nerlens Noel has blocked 23 shots that credited the closest defender as Luc Richard Mbah a Moute. It’s possible there are some labeling errors in the system but this could also just be the effect of players who come from out of area to block a shot over or around one of their teammates.

Here’s a bigger list of players who commonly are tracked as the closest defender when another player blocks the shot:

As you can see, lots of bigs who share the floor often have their shot altering misappropriated by SportVU — stat users beware and take note!