Remarks on Statistical Analyses of the NBA Play

In this entry I look at articles where statistical analysis is used to draw conclusions regarding NBA play. What the articles have in common is that there is something questionable about the points they make or about the underlying assumptions they apply.

Article 1: How many possessions will the new shot clock rule impact?

By Danial Massop for Nylon Calculus on Aug 25, 2018.

Points made in the article: NBA implemented a new rule that reduces “the shot clock after an offensive rebound from 24 seconds to 14 seconds”.

According to Massop’s analysis “over 30 percent of offensive rebounds result in putbacks”.  And “75 percent of offensive rebounds result in a possession that is five seconds or less.” And “only 6 percent of all offensive rebounds resulted in possessions that are 14 seconds or greater last year.”

Massop implies that the rule change only affects the portion of the plays that would have lasted for longer than 14 seconds if not for the rule change. He writes: “Given that we are only talking about a few seconds per game, the affect that this [rule change] will have on actual game play will be minimal.”

What’s questionable:  The rule change will affect at least 25 percent of the possessions after an offensive rebound. Arguably, the effect extends to all such possessions. Potentially, the change could end up affecting the offense-defense dynamics throughout the whole game.

According to Massop, 25 percent of the possessions after an offensive rebounds last six seconds or more. In that time, teams usually have started running a play – or something they have set up in advance. The rule change will affect these tactical choices and thus at least 25 percent of the possessions – not just 6 percent as Massop implies.

The offense does not anymore have the time to run regular set plays. Instead, they now must e.g. set up a quick hitter. Also, the offense will probably even more heavily favour putbacks and quick 3PA’s off kick-outs. The defense will also adjust to the short shot clock. They may e.g. decide to switch all screens.

The arguable part mentioned above regards this: Does the rule change affect the other 75 percent of the possessions after an offensive rebound – or the possessions that would have lasted no more than five seconds even without the rule change? Those possessions often end with a putback or a quick 3PA off a kick-out.

I argue that the rule change affects those possessions, too, because the change affects players’ decision-making process. That is because the rule change lowers the offensive players’ threshold to go for a putback or a 3PA off a kick-out.

The defensive players’ decision-making changes too. Since the value of the putbacks rises, the defenders may take more risks trying to block them. Also, they may close out more aggressively to the shooter after the initial kick-out.

Potentially, in the long run, the new shot clock rule may affect the NBA play even more profoundly. If the change turns out to lower the value of a possession after an offensive rebound, the teams may start going for the offensive boards more cautiously. That could affect the whole offense-defense dynamics throughout the game.


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