Saturday, January 21, 2017

Free Throw Deep Dives: Picking Your Spot

Note: Similar to my recent "deflategate" post, the following utilizes SportVU data on player and ball position. Sadly, this data was walled off from the public nearly a year ago, meaning what analysis I can do has a limited shelf life. This version of the post had been ready for some time now, but I had intended to expand its scope. However, given the data is nearly a year old, I thought it was best to publish what I had, even if I still consider it incomplete.

Part two of an infrequent series:

The purpose of these posts is to assess what makes for good free throw shooting. The NBA's SportVU system tracks the position of the ball in all three dimensions. I have taken that raw, often messy data and organized it using some freshman level physics. From that simple model, I have created a whole host of new descriptive statistics on player shooting mechanics.

In my first deep dive, I examined how vertical release angle (i.e. high arc, low arc) correlates with free throw success. As it turns out, there is little correlation between the arc of a player's typical shot and their accuracy. For every "high arc" sharpshooter like Stephen Curry, you have equally successful "low arc" shooters like Kyle Korver; or spectacularly unsuccessful high arc shooters like Andre Drummond. I did find a (unsurprising) correlation between consistency in release angle and free throw percentage.

In this post, we will shift focus from the vertical axis to the horizontal. Where do players typically "spot up" from the free throw line, and how important is it to pick a consistent spot?

Release Spot

We'll start with where players tend to release their free throw shot. For all the analysis below, I am using SportVU data going back to the 2013-14 NBA season and ending, sadly, on January 23, 2016 - the date the NBA removed detailed player tracking data from Also, I am excluding all games played at the Warriors' Oracle arena. For reasons unknown, the Oracle SportVU data is very messy and its inclusion was skewing player statistics, particularly those related to consistency.

The chart below shows the average release spot for some 326 NBA players (a player needed to have at least 100 free throws in order to be included).

Now that we are oriented, we will zoom in on the rectangular box:

Monday, January 9, 2017

Deflategate follow up: Game charts for all 30 NBA teams

In my NBA deflategate analysis, I shared charts for several teams that showed game by game coefficient of restitution for home games. Coefficient of restitution is a measurement of the ball's "bounciness". The point was to see if there is evidence of certain teams either over or under inflating their game balls.

As I called out in that post, there is no clear evidence of cheating in the data, but there do appear to be home teams that show a clear bias to one end of the bounciness range. You can see for yourself in the charts below which teams those are.

Each red dot represents a home game for the particular team. The gray dots are all NBA games for which I have data, and help provide context as to whether a team is an outlier.

Sunday, January 8, 2017

A Deflategate Analysis for the NBA

Phil Jackson, 1986:
"We'd try to take some air out of the ball. You see, on the ball it says something like 'inflate to 7 to 9 pounds.' We'd all carry pins and take the air out to deaden the ball. 
It also helped our offense because we were a team that liked to pass the ball without dribbling it, so it didn't matter how much air was in the ball. It also kept other teams from running on us because when they'd dribble the ball, it wouldn't come up so fast."

At its news cycle peak, the NFL's Deflategate scandal was inescapable. It even spilled over into the NBA, where admissions and accusations of ball tampering had been hiding in plain sight:
  • Marv Albert, in his 1993 autobiography, claiming to have seen future senator and presidential candidate Bill Bradley use a pin to surreptitiously deflate the ball as a member of the 1970s New York Knicks.
  • Bradley's teammate, Phil Jackson (quoted above), admitted to deflating balls in a 1986 Chicago Tribune article on cheating in sports.
  • Later, as an NBA coach, Jackson says he caught other NBA teams changing the pressure of the ball to better suit their playing style (e.g. the Magic Johnson-era Lakers trying to inflate the ball to nearly twice the allowed pressure to facilitate long rebounds and fast breaks)
  • Shaquille O'Neal, in the summer of 2015, says he used a needle to let air out of the ball during the Lakers' championship runs, claiming it helped him better palm the ball (he didn't think it gave him an advantage on free throws)
The NFL's Deflategate scandal was long on rumor and insinuation, but short on hard data (i.e. the makings of a good scandal). It boiled down to just 30 data points: two separate pressure gauge readings of 11 Patriots footballs and 4 Colts footballs, taken at halftime of the 2015 AFC Conference championship. You can breathe a sigh of relief, because I'm certainly not going to rehash that analysis here.

Instead, I will use not 30, but more than 2 million data points to analyze whether the NBA has a ball pressure scandal of its own.