NBA Players Need Their Rest: A Look at Shot Difficulty

As Krishna Nasru discussed in a previous article, days of rest naturally affect the physical performance of players. Following on this, I wanted to look at how the number of days of rest affects scoring.

Teams coming off of only one day of rest score an average 98.88 points per game; while teams coming off of 1+ days of rest score 100.36 points per game. Parsing that average beyond one day of rest, the points per game average stabilizes at 100.38, 100.56, 100.29 and so on. Consequently, teams on zero days of rest only win 46.55% of their games, compared to a 51.06% win percentage for 1+ days of rest.

Seeing these issues, I wanted to look for reasons beyond Krishna’s fatigue-confirming piece to find the answers for these downturns. Initially, looking at FGA and FTA per game showed no significant results, so I turned again to Krishna and his shot difficulty metric. I first looked at shot difficulty (measured as aXPPS) and the basic FG% against the league averages by days of rest (up to 3 days due to sample size).

There’s a startling difference between the days of rest, one that IS significant given the large sample size of shots from each bin. The more days of rest your team has, the better shots they’ll usually take.

However, the singular metric does not much say much as to why or how that is coming about. The following intends to answers that.

The numbers associated with days of rest are the difference from the league average found at the bottom. Essentially, a team with no days of rest between games shoots further away from the basket with slightly less distance from the closest defenders, earlier in the shot clock, and after more dribbles. It makes sense, for we would think that a more tired player would have these deviations from the respective means. Nevertheless, looking at shot distance without taking into account two-point and three-point shots does not make sense.

I checked to make sure there is no significant difference in three-point and two-point attempts between the days. That proved correct, so I looked at each distance filtered by shot type.

We can see that the shot distance difference for tired teams comes almost all from taking longer two-point shots, nearly universally recognized as an inefficient shot. Thus, tired teams are not only running less distance on the court, they’re shooting poorer shots.

Out of interest from Johannes Becker’s recent article on scoring possessions and scoring by quarter, I wanted to see how aXPPS and days of rest break down by quarter. This following is measuring the average away points minus the average home points per quarter:

The aXPPS formula gives a boost to home teams already, which explains why most differentials are negative, yet this still suggests that the difference in first quarter aXPPS is more pronounced than anywhere else. I’d be curious in seeing how Hannes’ numbers break down by days of rest, and how that correlates to this graph.

In sum, days of rest affect shot selection. This affect is most pronounced with 0 days of rest vs 1+ days of rest, which passes the intuitive test. The question now is how teams can combat this. Teams can either invest in improving rest or be forced to change their game plan to combat the tired tendencies.

Edit: See the follow up post for a deeper dive into the 0 rest games data