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Tuesday, March 6, 2012

NBA Analysis- Spacing

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BOSTON — Twenty-seven NBA teams are represented at the MIT Sloan Sports Analytics Conference, easily a record and the latest evidence that your team has fallen behind if it isn’t at least tinkering with advanced stats, data plotting, visual tracking, cutting-edge models to deconstruct the impact of fatigue on a player, and much, much more.
Visual tracking is among the most intriguing of such technologies. Ten of the league’s 30 teams have fully invested in a high-tech multicamera system, created by STATS LLC, that allows them to track every movement on the court — of players, ball and officials — in precise ways.

Analyzing space in a sophisticated way is one of the next crucial areas of NBA statistical development. Basketball is a spatial game in ways you don’t easily notice unless you re-watch film. Shooters create openings for teammates just by standing on the court. Non-shooters close those openings, but the smart ones, such as Shawn Marion, figure out how to use the space that defenders give them to create other openings that didn’t exist before.
Defenders who operate well — and in unison with their teammates — in open space can close gaps that inferior defenders don’t anticipate. Watch the way Nick Collison, for instance, slides off his man at the elbow to close off passing or cutting lanes before they come open. Or watch how the Dirk Nowitzki, an allegedly weak defender, slides just a few feet up from the baseline to help cut off a driving lane without moving too far so as to be unable to recover to his original position in time.
Quantifying stuff like this is very difficult, and it involves a huge combination of manpower and tech power. But teams that do it sooner — and more thoroughly — will learn interesting things.
All of this brings me to a research paper presented Friday that seeks to find the league’s best shooter. Harvard professor Kirk Goldsberry did this first and foremost by trying to quantify space. He took the section of the court from which about 98 percent of field goals are attempted — roughly a few feet behind the three-point line and in — and divided it into 1,284 squares, each comprising exactly 1 square foot. He then examined all field-goal attempts from the 2005-06 season through the 2010-11 season, placed each one of the 700,000 qualifying shots within one of those 1,284 squares and went about asking two questions:
1. Who has attempted at least one shot from the greatest number of squares? In other words: Who is confident he can score from basically everywhere?
2. Who can actually score efficiently from the largest number of those areas? For this question, Goldsberry crunched the numbers to find every square from which a shooter averaged at least one point per shot attempt over those six seasons. He used points per attempt rather than raw shooting percentage to properly account for the higher degree of difficulty — and the higher point value — of three-point shots.
The answers are both surprising and unsurprising. The player who has attempted at least one shot from the greatest number of those 1,284 squares? Kobe Bryant, who has jacked shots from 1,071 of them, better than 83 percent. (The empty squares, Goldsberry tells me, come from along the baseline behind the backboard and along the sideline where the three-point arc turns from a straight line into a proper arc. Kobe has obviously taken shots from near the latter areas, and if you used two-by-two squares, Golberry says it’s possible Kobe has the entire court covered).
Dwight Howard, not surprisingly, has attempted shots from only about one quarter of those squares. The rest of the top 10 after Bryant consists of eight wing players with range and one power forward. The wing players, in order from top to bottom: LeBron James, Vince Carter, Joe Johnson, Rudy Gay, Andre Iguodala, Ray Allen, Kevin Durant and Danny Granger.
The outlier? Cleveland’s Antawn Jamison, who has attempted shots from more squares than all but five of the above players. It makes sense, when you think about his combination of three-point range and awkward flip shots.
But does Jamison actually shoot efficiently from a lot of those places? Does he hit the one-point-per-attempt minimum that Goldsberry used to find the players who shoot most effectively from the most squares?
The league’s top shooter, by this second measure, is Steve Nash. The Suns’ point guard hit the one-point-per-attempt minimum from 406 of 1,284 squares, or 31.6 percent, during this six-season span. Allen is next, with 386 qualifying squares, followed by Bryant at 383. Bryant’s presence here is a reminder that despite his occasional selfishness and questionable shot selection, he remains a prodigious and varied scorer the likes of which we rarely see.
Three names appear on this efficiency top 10 that did not appear in the shot distribution top 10: Paul Pierce, Nowitzki and Rashard Lewis. The first two are not surprising. Pierce and Nowitzki are fantastic shooters, and Pierce has gotten more efficient from three-point range since the Celtics surrounded him with All-Star teammates in Kevin Garnett, Ray Allen and Rajon Rondo.
But Lewis? If you watched him in Orlando regularly, you saw that he was a bit more than a spot-up three-point gunner even in a system that essentially asked him to be a spot-up three-point gunner. He has a nifty post game that he can use against smaller players, and he loves to work with his back to the basket from the left baseline. Still, Lewis’ appearance in the No. 5 slot on this list is surprising, even if the database includes his last two seasons in Seattle, where he worked as a more traditional all-around scorer.
Also a mild surprise: Gay, checking in at No. 9. Read a piece of data like this, and you can see why Memphis has real hope that the 25-year-old forward can emerge as a legitimate scoring star.
Again, this paper is just the tip of what is being discussed here in terms of space and basketball. Another paper looks at hundreds of thousands of rebounds to see where they go, who snares them and how high the ball is off the floor when someone finally grabs it. One little nugget from that paper: It appears the conventional wisdom that corner three-point attempts are more likely to rebound over the opposite side of the rim is incorrect. Corner threes have a seemingly random rebound distribution, like any other three-point shot.
Another tidbit: Mid-range shots are least likely among all shot attempts to result in an offensive rebound. That makes some intuitive sense. Shots taken near the rim tend to fall close by, where lots of big men, including the original shooter, can pursue them. And three-point shots, with the speed they gain in the air, really do seem to result in longer rebounds that offensive players are more likely to get. But the decline in offensive rebounding rate for mid-range shots is larger than we’d expect, a conclusion that could lead a coach to minimize such attempts even more.

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