Sunday, February 7, 2016

Are there "shooter friendly" NBA arenas?

Baseball, in contrast to most every other major sport, allows each team significant leeway in designing their home venue. Both the length and height of home run fences varies from park to park. In addition, regional differences in air density and humidity can have a significant impact on how far a baseball travels in flight. 

As a result, there are what is known as "hitters parks" such as the Colorado Rockies' Coors Field, where the thin Denver air results in more than two runs per game on average. And there are "pitchers parks", like San Diego's Petco Park, with its dense, dry sea-level air and distant home run fences that lead to, on average, roughly one less run scored per game.

Does a similar phenomena exist in the NBA? Are there "shooters arenas"? Of course, the NBA maintains far more uniformity across its venues than the MLB. The dimensions of the court do not vary, the free throw line is always 15 feet from the backboard, and the three point line is the same distance everywhere (basketball brainteaser: If you were playing the Warriors and given the option of re-drawing the three point line, would you make the line closer, or further away?). 

Saturday, February 6, 2016

NBA Games are not Getting Longer

With the NBA continuing to expand the types of plays subject to instant replay review, there was justifiable concern that these changes could lead to even longer games. I've done a lot (perhaps too much) research into the length of NBA games and what drives it, starting with a post on the average length of each minute of NBA game time. Subsequent work looked into the difference between close games and blowouts and the length of playoff games. Also check out the "Significant Other" calculator that is part of this site's live win probability graphs.

The NBA, never shy with the sharing of data, thoughtfully timestamps each play of every NBA game, which aids and abets all the aforementioned research. For this post, I will use those timestamps to examine trends in average game time, spanning the past six seasons. Were the fears of longer NBA games justified?

As it turns out, games are shorter than they were just a few years ago. And the expansion of instant replay does not appear to have made a noticeable impact on game length.

Sunday, January 31, 2016

Home Court Advantage: Free Throw Shooting

The King emerges from behind Arizona State's
"Curtain of Distraction"
This is the first in a series of posts on home court advantage in the NBA. Each post will examine home court advantage from a specific statistical angle.

Home court (and home field) advantage may be one of the most documented and replicated phenomena in the field of psychology. It shows up in every major sporting competition: soccer, football (professional and collegiate), baseball, college basketball, and the NBA. There is a wealth of statistics supporting its existence, literally spanning three centuries.

Since 2010, home teams in the NBA have won 59% of their games, with an average point differential of 2.8 points. While home court advantage has been on the decline, relative to the veritable coach and buggy days of the 1970's (see this chart from ESPN's Tom Haberstroh), rumors of its eventual demise may have been exaggerated.

At this point in the season last year, home teams had an all-time low winning percentage of just 53.7%. It appeared we were in the midst of a home court advantage sea change. NBA teams were finally winning the road battle, thanks to advanced biometrics, disinterested crowds, and sweet, sweet chartered jets.

Saturday, January 23, 2016

San Antonio's stinginess in transition

The San Antonio Spurs currently lead the league in defensive efficiency, allowing just 95.3 points per 100 possessions, according to Basketball Reference. With the league averaging 105.1 points per 100 possessions overall, the Spurs are ten points above the league average on defense. They are better at defense than the Warriors are on offense, as Golden State is currently nine points above the league average, with 114.3 points per 100 possessions.

To illustrate what an outlier the Spurs are on defense, I will use the advanced per possessions statistics tool to examine the Spurs' defensive efficiency and what drives it. Here is a chart for overall defensive efficiency (note that these numbers differ slightly from basketball reference, due to oddities in the play by play data and the exclusion of technical foul points).

Wednesday, January 6, 2016

The Vegas Playoffs

Inspired by numbers shared by Cousin Sal on Monday's Bill Simmons podcast (and idle curiosity), I decided to reseed the NFL playoff field according to record against the spread, as opposed to win-loss record. There is literally no point to this exercise, but when you have spent hours coding the NFL's excessively redundant tiebreaking procedures like I have, you're on the lookout for any way to justify your time down in that hole.

Here is the AFC Vegas playoff field:

Sunday, January 3, 2016

Heroes, Goats and Garbage Men : New Clutch Shooting Reports

Clutch shooting isn't easy, and neither is defining it. The NBA defines clutch shooting as any shot taken in the last five minutes of the game in which the score differential is within five points. For this post, I will introduce a new interactive tool that uses my win probability model to classify shots into four categories: Garbage Time, "Normal" Basketball, Clutch Situations, and "Double Clutch" situations. With these four new shooting categories, we can dive deep into which players are taking and/or making the most clutch shots.

As I called out in a previous post on clutch performance, there is nothing inherently wrong with the NBA's definition of clutch performance. There's something to be said for easily applicable rules that are simple to explain. However, a shot taken in the final minute when your team is up by five doesn't feel quite as "clutch" as a three pointer in the final 10 seconds with your team trailing by two. Fortunately, we can use win probability to create a more nuanced version of clutch, and one that better aligns with what one would expect a clutch situation to be.

Thursday, December 31, 2015

2015 Early Season Power Rankings - The Results

In which we rank the rankings...

Power rankings are everywhere, but how do we know if they are any good? If they are intended to be predictive, we can test them for their predictive value. So, for the past three years, I have archived a cross section of power rankings from early in the NFL season (after week four). Then, once the season is done, I assess each ranking's accuracy in predicting future wins in that same season.

Each team's win percentage for weeks 5-16 (week 17 excluded) is rank ordered. This is then tested for agreement with each power ranking. I use the Spearman Rank Correlation coefficient for this purpose. A Spearman value of 100% would indicate perfect agreement between two rankings (e.g. if 1-32 in win percentage lined up identically with the power ranking in question). A value of -100% would indicate complete disagreement between the two lists, meaning 1-32 in win percentage lines up with 32-1 in the power ranking. A value of 0% would mean, roughly, no correlation between the two rankings.

I archived the week 4 power rankings in this post from October. As a reminder, the rankings I evaluate are: Football Outsiders DVOA, ESPN's FPI (as a replacement for Brian Burke's AFA efficiency rankings), the Simple Ranking System, ESPN's official NFL power rankings, FiveThiryEight's Elo rankings, and the Betting Market Rankings published here at inpredictable.