Sunday, July 17, 2016

Betting Market Rankings for the WNBA

The WNB-Ays
I have added the WNBA to my suite of betting market rankings, to go alongside those for the NBA, NFL, MLB, College Football, and College Basketball. The purpose of these rankings is to reverse engineer an implied power ranking from the Vegas point spreads, essentially distilling the combined wisdom of the market.

Here are the rankings as of July 17:


GPF stands for "Generic Points Favored". It is what you would expect a team to be favored by against a league average opponent on a neutral court. By combining the betting over/under with the point spread, I can decompose GPF into its offensive and defensive components, oGPF and dGPF (note: offense and defense are on a points allowed per game basis, rather than points per possession - there is no way to derive implied per possession metrics from the betting data). GOU stands for "Generic Over/Under" and it is what you would expect the betting over/under to be for that team when playing an average opponent.

Saturday, July 16, 2016

Bonus Tim Duncan Chart - Bank Shots

On the occasion of Tim Duncan's retirement earlier this week, I used SportVU motion tracking data to call attention to an unnoticed element of his game: his low and tight, line drive shot arc.

Using that same data, we can also delve into a more well known aspect of Duncan's shooting game: his bank shot. For the bank shots I am able to identify, the chart below shows where Duncan's bank shots hit the glass. For comparison purposes, I also have a chart for all NBA bank shots.
Duncan seemed to favor the upper left portion of the glass, especially compared to the league average, which is clustered far more in the center, just at the top of the backboard's inner square.

On an unrelated note, I noticed that there appears to be a bias to when a scorekeeper will classify a shot as a bank shot, and that bias is skewed towards made shots. I have found several examples where the motion tracking data clearly shows a missed bank shot, but the official shot description does not call it out. For that reason, I would be skeptical of any stat that shows a particular player is far more effective when shooting bank shots.

Once I have the methodology cleaned up, I hope to use the SportVU create a deeper dive into the bank shot and the underlying physics (similar to last summer's post on the effects of air drag on a basketball's trajectory).

Monday, July 11, 2016

The weirdest thing about Tim Duncan

Tim Duncan announced his retirement today, after 19 seasons in the NBA. On Duncan and his impact to the game, there is no shortage of articles, retrospectives, and in-depth analyses (statistical and otherwise) from which to choose today, most pre-written, no doubt.

Duncan was famous, paradoxically, for not attracting attention to himself, and his retirement announcement was no exception. Contrast Duncan's brief, matter of fact press release (not even a press conference) to Kobe's season long, air ball ridden farewell tour. I wonder how far off the Onion's version of Tim Duncan is from the real thing: Tim Duncan Raving About Health Benefits of Standing Bench, Tim Duncan Around if any Spurs Have Questions About Sequester, Tim Duncan Sends Teammates Google+ Invitations for Fifth Straight Day (I will miss the Onion's Tim Duncan almost as much as Uncle Joe Biden).

But behind Tim Duncan's staid, middle of the road public persona lies a hidden deviancy: his shooting arc.

Using location data tracked by the NBA's SportVU camera system, we can analyze player shooting mechanics in exhaustive detail. For more background, see my introductory post on this topic from last year, as well as some more recent research on free throw shooting.

Monday, June 20, 2016

Inspired by last night's game 7, a new metric: The Tension Index

Tightrope walkingPrior to Sunday night's game 7, I lamented the lack of in-game drama in this year's NBA finals. The average excitement index of those six games was 4.77, which at the time was the lowest average for the finals in the past 10 years. Game 7, however, delivered on the hype, registering an excitement index of 8.6, and bringing the series average up to 5.32.

While 8.6 is well above the typical figure for an NBA game, it ranked 185th out of 1,316 NBA games this season, and was just the 13th most "exciting" game of these playoffs. But that doesn't feel quite right. There is a type of "excitement" that isn't necessarily captured by the excitement index.

Sunday, June 19, 2016

Exciting Finals, Boring Games

Regardless the outcome in tonight's game 7, we are guaranteed a compelling story. Either the "jump shooting" Warriors put a capstone on their record setting 73 win regular season, or Lebron James and the Cavaliers end the longest championship drought of any major American city.

At a macro level, the 2016 Finals has had more than its share of drama and excitement, allowing for the hot take cannon to swing wildly in all directions, firing indiscriminately as the outcome of each game seemed to flip the prevailing narrative.

But when it comes to action on the court, the 2016 NBA finals have been the most "boring" of the past 10 years, at least by one measure. For each NBA game, we can use this site's win probability model to calculate an "excitement index". The index measures how much the win probability graph "travels" over the course of the game. It's a concept I stole adapted from the now-defunct win probability graphs from Advanced Football Analytics.

The 2016 NBA finals have been largely devoid of any late game heroics that can lead to wild win probability swings. The average excitement index for this year's Finals is 4.77, which, barring a more exciting game 7, would be the lowest in the last ten years, beating the 2014 NBA Finals in which the Spurs beat the Heat handily in five games (average excitement index: 4.79). The most exciting championship round of the past 10 years was the 2011 Finals between the Heat and the Mavericks, with an average excitement index of 7.17.

The most exciting NBA finals game of the past 10 years was game two of the 2015 NBA Finals, in which the Cavaliers stole home court advantage from the Warriors in overtime. The second most exciting Finals game was game 6 of the 2013 Finals, featuring Ray Allen's buzzer beater, amongst many other memorable plays.

The chart below shows excitement index for each NBA Finals game from the past 10 seasons. We are definitely due for some late game drama.


Monday, May 30, 2016

Is pace contagious?

Possessions, despite being analytical bedrock, are not an officially tracked NBA statistic. As a result, the counting of possessions in an NBA game has historically been indirect. We tease them out of the box score by counting the ways a possession can end, like physicists searching for the Higgs boson by tracking the particles into which it immediately decays[1].

This indirect measurement has limited our ability to understand how pace works in the NBA, and who controls it. The box score can tell us that the Golden State Warriors play at a very fast pace, and squeeze in an above average amount of possessions into 48 minutes of regulation play. The Warriors are clearly fast on offense, but does that spillover into their defense? Do their opponents get caught up in the Warriors' hectic flow?

Sunday, May 8, 2016

Endgame strategy in the NBA

Or how I learned to stop worrying and love the #quick2 (sometimes).

When a team is trailing by three late in a game (e.g. less than 30 seconds left), are they better off going for a tie with the three pointer? Or is the superior strategy to attempt a quick, high percentage two point shot, and hoping for a turnover or missed free throws on the ensuing possession?

The "quick two" approach draws plenty of derision from my analytics-heavy Twitter feed. Probably because it's emblematic of the conservative, risk averse thinking that mars strategic decisions across a number of sports. Football coaches punt too often on 4th down. Baseball managers still call for the sacrifice bunt, even though it reduces run expectancy. And NBA teams were historically slow to embrace the three point shot.

But punts, bunts, and three pointers have all been thoroughly analyzed from a statistical perspective. As far as I know, no one has run the numbers on whether that quick two really is a suboptimal strategy. In this post, I will examine which strategy leads to victory more often. I'll start with teams that trail late by three points, and then look at the same situation, but when trailing by four.