Optical Tracking Data and the importance of screening in the Boston Celtics’ offense

Perhaps the star presentation of the 2011 Sloan Sports Analytics conference was Sandy Weil, who two years ago dropped a bomb on the NBA community by proclaiming, with copious data to back him up, that the “hot hand phenomenon” simply does not exist.

If Weil’s 2009 presentation made people reconsider elements of the epic opening round series between Chicago and Boston (take that, Ben Gordon!), his 2011 presentation reminded me immediately of the current Celtics team.

This year, Weil and the people of STATS, LLC brought less conclusive, but maybe more provocative thunder to Boston, with a presentation titled “The Importance of Being Open: What Optical Tracking Data Can Say About NBA Field Goal Shooting.” Weil explained how cameras in the rafters of a few NBA buildings were capturing every movement of every player and producing data about how teams move, pass and score. For a more full explanation of why this technology will change the way we analyze basketball, read this report from Brett Hainline.

Here’s what Hainline pulled as the salient takeaways:

The three primary results of Weil’s poring through the data and accounting for things like historical player shooting percentages, distance, and shot type:

  • Tight defense (within three feet) drops expected shooting 12 percentage points (a 50 percent shot becomes a 38 percent shot).
  • Field goal percentage drops one percentage point for every 1.5 feet from the rim.
  • There is something beneficial about the catch and shoot, beyond expectations.

It’s that last one that is most fascinating to me: There is now empirical proof that crisp ball movement can result in a better outcome for the offense. Weil’s data shows that even when accounting for the defender’s proximity, the field goal percentage on catch and shoot plays was higher than expected for the distance of the shot. The new optical data is detailed enough to give the knowledge of how a player got the ball, how long he had it, what the last action was before a shot (dribble, pass, etc), and where the defense was a second before a player received the ball and then as he catches it.

Ray Allen comes clean off a great screen from an unpictured and under-appreciated teammate

As I observed Weil’s presentation, visions of wide open Celtics hoisting catch-and-shoot twenty footers or rolling open to the rim flashed before me. Indeed, the Celtics offense seems like a manifestation of what Weil identified as the ideal way to score in the NBA. Currently, the Celtics take fewer shots each game than any team in the league, yet they still manage to shoot the seventh most attempts at the rim. From this ideal distance, the Celtics score the second most buckets in the league (again, doubly impressive because of their low overall shot attempts), on the league’s hightest FG% and Assist Rate (the percentage of made baskets that were assisted by a teammate)– all figures consistent with the conclusions of Weil’s presentation.

Aside from these relative gimmes, the Celtics also attempt a disproportionate amount (11th most) of 16-23 ft. field goals. Typically, the long two is considered the worst shot in basketball.  But Boston manages to shoot a relatively high percentage at nearly 41%, perhaps because 70% of those makes come off assists (and by extension, in catch and shoot situations). The grinding machinery of the Celtics’ baseline screen sets and pick and pops generates excellent deep two looks for guys like Paul Pierce, Ray Allen and especially Kevin Garnett, who’s made an unreal 48% of his attempts from that range, 90% of which have been assisted (All stats per HoopData.com).

Now take a look back at the conclusions Sandy Weil drew in his presentation. The Celtics have dead-eye midrange shooters, but Weil’s evidence suggested that the expected value of an open 18 footer is just as high as a more closely defended 14 footer. The Celtics are also clearly producing a singularly high amount of catch and shoot opportunities, getting a tremendous proportion of their shots very close to the rim, and the human eye test suggests that when they can’t get inside, they are able to create wide open shots elsewhere on the court.

Weil’s data, in concert with a Celtics offense that offers a real world model for STATS, LLC’s findings, suggests a great value in an under appreciated kind of shot creation. Typically, the argument over shot creation centers around whether players can create efficiently for others off the dribble. But Weil’s presentation indicates that the ability to free a player for a spot-up jumpshot by setting a viscous screen, something just about every Celtic, including the 170 lb Rondo, does exceptionally well, also has tremendous value—and will soon be measurable.

Once obscure statistics like rebounding rate have gained prominence since advanced metrics have shown their merit. In coming years, Optical Tracking Data will exponentially increase our ability to analyze the minutia of on court movement, like screening, to explain how Ray Allen finds himself so open. If great screeners create great catch and shoot opportunities, and those are the best field goal opportunities, then what player’s screens get players most open, most often? Who are the superstars of screening?

We haven’t seen the numbers, yet. But I’m willing to bet that the Celtics, who lead the league in FG% and Assist %, would be tops in screening efficiency, too.

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