Is hockey simply too dangerous to play?

That was among the questions raised last week by the news that the brain of the late hockey player Bob Probert showed evidence of chronic traumatic encephalopathy, a degenerative disease caused by repeated concussions.

The question is already being asked of football, the team sport with the highest rate of concussion, according to medical and neuropsychological researchers. Hockey has the second-highest rate.

“Of course, the ideal number of concussions would be zero,” Gary Bettman, the commissioner of the National Hockey League, said at the league’s all-star game in January while noting a slight rise in the concussion rate this season. “Our objective is to come as close as possible to getting that result without changing the fundamental nature of our game.”

But what is the “fundamental nature” of hockey? Does it include checks to the head? Fighting?

It is not always easy to say how much you can reduce the violence in a sport without losing its essence.