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.

Sunday, April 24, 2016

New box score feature: Pace and Efficiency Report

I have added a new feature to my NBA Win Probability Graphs and Box Scores. If you click the "pace" tab, you will see a table that looks like this:


Using the play by play data, this table summarizes offensive pace, as measured by seconds per possession. The "season" row shows each team's average offensive pace for the season. The "opponent" row shows how each team's opposing defense has controlled the offensive pace this season. Similar statistics are shown for scoring efficiency, as measured by points per 100 possessions. This is basically a game-specific version of the team summary pace tool I rolled out last season.

The table above is from Game 3 of the 2015 NBA Finals, in which the Cavaliers took a (fleeting) 2-1 series lead over the Warriors. The Cavaliers' success in that game, and the game prior, was often credited to slowing the tempo of the notoriously fast-paced Warriors. But what the table shows is that while Cleveland certainly slowed their own pace on offense (from 15.9 seconds to 17.0), the Warriors were still playing their game on offense, mostly. They averaged 13.9 seconds per possession, just slightly above their season average, and still well below the league average of 15.1 seconds.

Just a note on the possession counts: These do not precisely align with those you find on sites like basketball-reference.com. In general, I am counting more possessions on average than what is usually tallied using the box score, which results in slightly lower efficiencies. The main reason for this, I believe, is that my method counts "end of quarter" possessions that do not result in a typical box score "possession marker", like a made/missed shot or a rebound. If a team gets the ball with 10 seconds left and fails to get a shot off, that will likely not count as a possession using the box score stats, but is counted as such by my method.

Eventually, I hope to add pace and efficiency for the other possession types to this feature: after made shot, after defensive rebounds, and after turnovers.

Saturday, April 16, 2016

The 2015-16 NBA Regular Season Review

Using the various NBA tools I have built for this site over the years (see the sidebar on the top right), here are the top performers, top performances, top games, and team superlatives from the 2015-16 season.

Player awards

For the most part, I'm judging players according to win probability added (WPA), which is an admittedly limited metric (it only accounts for made/missed shots, free throws, and turnovers).
  • Most Valuable Player - Stephen Curry led the league with +10.59 win probability added. Kevin Durant came in a distant second with +8.01, an MVP-worthy total in just about any other season. Here is how Curry's progress compares against the top WPA finishers of the past seven seasons (an update to this post):
  • Least Valuable Player - Rajon Rondo. -4.96 WPA. Granted, this excludes Rondo's other box score contributions, such as assists (where Rondo ranks second in assist WPA) and steals, where he ranks in the top ten.
  • Most Improved Player - The player with the single biggest leap in WPA from 2014-15 to 2015-16 was Kevin Durant, but that "improvement" was due to his injury shortened season last year in which he played just 27 games. If we set Durant aside, the most improved player this year was.......Steph Curry. Curry won the MVP award last year with +5.75 WPA, and nearly doubled down on that mark this season.

Saturday, April 2, 2016

Playoff Seed Probability Motion Charts

With an 82 game season, an NBA team's fortunes then to ebb and flow in increments, rather than huge leaps. This gradual evolution can make for some interesting motion-chart visualizations. For example, there is Aaron Barzilai's animation of the Warriors pursuit of the single season wins record. Or this visualization of the evolution of the win percentage of the NBA's top four teams.

And as I have done the last couple seasons, here are motion charts that show how each team's playoff seed probabilities have evolved and shifted over the 2015-16 season. The probabilities are calculated using my NBA Vegas rankings, which update daily and re-project the remainder of the season and resulting playoff seeds. Time permitting, I will update the chart with the latest results, up until the end of the regular season. Just check back at this same post.