Saturday, October 6, 2018

The Impact of the New 14-Second Shot Clock Off of Offensive Rebounds

Arguably the biggest rule change this offseason in the NBA is the implementation of the 14-second shot clock off of offensive rebounds:
A team grabbing the rebound of its own missed shot has been given the full shot clock. Under the new rule — in effect in the NBA G League since 2016-17 and international basketball since 2014-15 — the clock will go to 14 after an offensive rebound of a missed shot or free throw that hit the rim.
The rule change aims to speed up the pace of play (especially in late game situations), but how many plays will it really affect? Through BigDataBall I acquired 7 seasons of NBA play-by-play data (from 2010-11 to 2016-17, graciously hosted on a coworker's Raspberry PI in a PostgreSQL database) and looked at all possessions that resulted from an offensive rebound in the regular season. It won't affect many of them:

95.2% of all possessions off of an offensive board finish in 14 seconds of less already, even with a full 24 second shot clock. But what happens in those possessions?

For the shorter possessions, it's not surprising that teams are getting quality looks and making them more often than not (usually on a putback). But for the possessions that drag on, the quality of basketball is clearly worse. Missed shots + fouls + turnovers make up 57.9% of the short possessions, but happen 65.2% of the time when they stretch beyond 14 seconds.

What about the late game situations where the game is close? I also looked at all possessions that occurred with < 1 minute left and the score within 6 points:

93.6% of these possessions finish in 14 seconds or left, which is a slight decrease from the rest of the game. However, this specific situation only occurs over 1.7% of all plays off an offensive board (3,158 out of 180,830). That being said, fouls do occur more often, as you would expect:

Teams foul 16.6% of the time here, compared to 12.7% on all possessions. So in close end game situations with a shorter shot clock, will the trailing team foul less since they can get the ball back 10 seconds earlier? A missed shot is already the most likely outcome, so this behavior should be even more incentivized now. The 2018-19 season should bear this out, but you probably won't notice an impact on most games.