Klay Thompson, the star shooting guard for the Golden State Warriors, unambiguously took a knee to the face in the team’s Wednesday night game against the Houston Rockets. After that, everything got a little muddled — not only for Thompson, but also for the doctors who are being asked to explain why their test didn’t keep him out of the game.
The team’s doctors gave Thompson a concussion evaluation after the injury and cleared him to return to the game. Thompson didn’t get to play (he was still bleeding and wasn’t allowed on the court), and now that looks like a lucky break. In a postgame interview, Thompson said he was “feeling a little dizzy,” and the team confirmed that after the game, he had concussion-like symptoms and will need to be retested before he can play in future games.
The NBA concussion protocol requires any player who is suspected of having a concussion to have an immediate neurological evaluation. The NBA uses both a modified version of the Sport Concussion Assessment Tool (SCAT) and the Cogstate Computerized Cognitive Assessment Tool (CCAT). And according to their clinical trials, both tests do pretty well at detecting concussions accurately.
The SCAT combines the results of tests of balance, cognitive function and other concussion indicators into a single score. According to a 2015 study, the SCAT has a sensitivity (successfully detecting concussions in people who really have concussions) of 96 percent. The NBA’s modified SCAT is probably somewhere in the same ballpark, but it’s hard to know for sure because the league hasn’t made public its modifications to the test. The study used a threshold of a 3.5-point drop from an earlier, baseline SCAT score to identify a concussion. If the NBA uses a different figure or focuses on a SCAT subscore instead of the overall figure, the accuracy of the test might change.
The CCAT is a computerized test (you can try out a practice version here) that gives players four tasks (sort cards by color, remembering which cards you’ve already seen, etc.) and checks to see if they do badly on at least two of the challenges. According to a 2014 study, the CCAT successfully flags 96 percent of players who really have concussions.
So, if the tests are pretty accurate, why wasn’t Thompson identified as possibly concussed until after the game?
It’s hard to say, especially without information on the NBA-specific protocols, but sometimes tests are less accurate in real life than they are in a trial. Or a concussed player could just be unlucky; 5 percent or so pass a screening test in error.
If Thompson hadn’t mentioned that he felt ill, questions might not have been raised about whether the test failed. Players are a check on the test, but they may not feel free to speak up if they’re passed in error.
What happened to Thompson is a reminder for the NBA to audit its methods to make sure that the assessments it is giving players are working as well as they did in the clinical trials. That way, players can trust their doctors, and the fans can trust the league.
Update (3:25 p.m., Friday, May 29): On Friday afternoon, the Warriors said Thompson had suffered a concussion, and would not return to the court until he is symptom-free and cleared under the NBA’s concussion protocol guidelines.