Coach’s challenges: a user’s guide

Be like the Knicks, not the Spurs

In our Monday editorial meeting, David Thorpe was excited about coach’s challenges. He was telling the story of the incredible end of Sunday’s Raptors-76ers game. Every one of three coach’s challenges over the final 13 seconds resulted in Raptors ball, and the Canadian team won by a single point because of them.

Thorpe’s point: those coach’s challenges were not annoying delays. They were fun. His idea: keep everything the same as it is right now, but make it so coaches can only challenge calls in the last two minutes of games within 15 or 20 points or whatever number is fairly considered winnable by both teams.

This got me wondering how coach’s challenges are working right now. Thorpe is correct that we tend to see them as end-game tools, even though they have a much higher rate of success earlier in the game.

The league publishes a big ugly spreadsheet of every single coach’s challenge. I’m as nervous as everyone else about our AI future, but have also been consulting smart people about deft applications, and in this case fed the league’s whole dataset into Google’s Notebook LM, which was able to quickly extract answers to useful questions.

For example:

And yet:

Some coaches are especially prone to saving their challenges until the end of the game. The Magic, 76ers, and Rockets hoard for the final minutes. That can pay off in a major way, but comes with an obvious downside: it means you don’t use your challenge on the game’s most obvious blown calls. Picking from a smaller group of plays results in a far lower success rate.

Then there’s the matter of what kinds of calls you challenge. You want to challenge calls that video can clarify. My AI colleague drummed up some data from the NBA’s spreadsheet of the league’s 849 coach’s challenges through January 11:

The video evidence of who touched the ball last is almost always crystal clear. Whether or not someone committed a foul, though, gives the referees a lot more leeway for interpretation, and arguably, as they are human, they show a certain affection for keeping to the earlier call.

Not every team seems to have their strategies together.

The Spurs are especially terrible at using their coaches challenges, having succeeded literally just five times all season. Compared to the Wolves’ 31 successful challenges, this is an incredible wasted opportunity. 81 percent of Knicks’ challenges succeed, compared to 26 percent from the Spurs. It’s hard to believe the Spurs couldn’t have extra win or two if they got better at this. The NBA data shows that the Spurs don’t challenge often, and when they do it’s often in tough categories like defensive fouls and goaltending. They also save their challenges until late in the game, and then use them on plays that are not overturned.

There’s more to think about. Not all reversals come with the same prize. Let’s say your defender was called for a defensive foul guarding a shooter who nailed a 3, and now has a shot at a four-point play. If that’s reversed to an offensive foul because the shooter kicked his leg out, the reversal is four points and the ball, which is the promised land of coach’s challenges. On the other hand, there are times when the ball goes out after an uncalled foul, and the successful challenge results in what was going to happen anyway: the ball out of bounds.

Challenges can be valuable in nullifying foul trouble. The NBA’s spreadsheet does not name the players involved, so it’s hard to assess which teams are good at that, but watching games it seems almost certain that coaches are more likely to challenge the call that gets their star in foul trouble, or ejected.

There’s a bigger picture lesson from this: about 60 percent of challenged calls are overturned. How does that make you feel about the accuracy of NBA refereeing generally? This is a biased selection, but surely this implies there are many mistaken calls all game long that don’t get challenged. In Part 2: Why the coach’s challenge is a silly way to correct the referees, and why it might be on the way out anyway.

---

Thank you for reading TrueHoop! More on coach’s challenges tomorrow …