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.

Saturday, December 24, 2016

Guess the Lines - Final Results

Here are the week 16 results for the final installment of "Guess the Lines". This is a weekly feature in which I put my Vegas NFL rankings to the test by predicting the point spread of upcoming NFL games. I compare the accuracy of my prediction against those of Bill Simmons and Cousin Sal, as featured on their weekly NFL podcast. In addition, I also calculate an implied point spread from ESPN Chalk's weekly Vegas NFL rankings.

I'm not sure if Bill and Sal intend to do a Week 17 podcast, but I've decided to halt the prediction contest at Week 16. Week 17 lines can be a bit wonky due to teams that don't have anything to play for.

Here are the week 16 results. Bill Simmons wins this week with a mean absolute prediction error of 0.84 points.

Friday, December 23, 2016

Turnover Index Week 16

Here are the Turnover Index picks and results for week 16. The Turnover Index is a simple betting strategy based on the theory that the market overvalues defensive turnovers when judging team strength. See here and here for more background.

We went 0-1 with our single Week 14 bet, and our bankroll dropped by $17 from $1,023 to $1,006. We are now 6-7 against the spread on the season, with an ever so slightly positive ROI of 0.5%. Bets are sized according to the Kelly criterion.

Here are the 2016 season to date results:

weekbetswonstarting
bankroll
amount betprofitsending
bankroll
6 1 0 $1,000 $36 (3.6%) ($36) $963
7 1 1 $963 $10 (1.1%) $9 $973
8 1 1 $973 $38 (4.0%) $35 $1,008
9 3 2 $1,008 $64 (6.4%) $51 $1,060
10 2 1 $1,060 $15 (1.5%) ($7) $1,052
12 2 1 $1,052 $13 (1.3%) ($6) $1,046
13 2 0 $1,046 $23 (2.2%) ($23) $1,023
14 1 0 $1,023 $17 (1.7%) ($17) $1,005

Saturday, December 17, 2016

Guess the Lines Week 16

Here are the week 15 results and week 16 predictions for this installment of "Guess the Lines". This is a weekly feature in which I put my Vegas NFL rankings to the test by predicting the point spread of upcoming NFL games. I compare the accuracy of my prediction against those of Bill Simmons and Cousin Sal, as featured on their weekly NFL podcast. In addition, I also calculate an implied point spread from ESPN Chalk's weekly Vegas NFL rankings.

Here are the week 15 results. Cousin Sal wins this week with a mean absolute prediction error of 0.94 points.

Saturday, December 10, 2016

Turnover Index Week 14

Here are the Turnover Index picks and results for week 14. The Turnover Index is a simple betting strategy based on the theory that the market overvalues defensive turnovers when judging team strength. See here and here for more background.

We went 0-2 with our Week 13 bets, and our bankroll dropped by $23 from $1,046 to $1,023. We are now just 6-6 against the spread on the season, with an ROI of 2.3%. Bets are sized according to the Kelly criterion.

Here are the 2016 season to date results:

weekbetswonstarting
bankroll
amount betprofitsending
bankroll
6 1 0 $1,000 $36 (3.6%) ($36) $963
7 1 1 $963 $10 (1.1%) $9 $973
8 1 1 $973 $38 (4.0%) $35 $1,008
9 3 2 $1,008 $64 (6.4%) $51 $1,060
10 2 1 $1,060 $15 (1.5%) ($7) $1,052
12 2 1 $1,052 $13 (1.3%) ($6) $1,046
13 2 0 $1,046 $23 (2.2%) ($23) $1,023

Guess the Lines - Week 15

Here are the week 14 results and week 15 predictions for this installment of "Guess the Lines". This is a weekly feature in which I put my Vegas NFL rankings to the test by predicting the point spread of upcoming NFL games. I compare the accuracy of my prediction against those of Bill Simmons and Cousin Sal, as featured on their weekly NFL podcast. In addition, I also calculate an implied point spread from ESPN Chalk's weekly Vegas NFL rankings.

Here are the week 14 results. Bill Simmons wins for the second week in a row, with a mean absolute error of 1.00 points.