The determination that the hockey enforcer Derek Boogaard had a degenerative brain disease linked to repeated hits to the head when he died in May at age 28 has fueled a debate among medical experts over whether the sport should ban fighting.

The National Hockey League commissioner, Gary Bettman, has played down the findings announced this month by Boston University researchers that Boogaard had chronic traumatic encephalopathy, a close relative of Alzheimer’s disease known as CTE. He said data on the causes of brain trauma were insufficient to warrant stiffer penalties for fighting.

Dr. Ruben Echemendia, a former president of the National Academy of Neuropsychology, advises Bettman as the director of the concussion working group formed in 1997 and operated jointly by the NHL and the players union. He agreed with Bettman’s position, saying there is not enough scientific evidence to justify rules changes that would curtail or end fighting in the NHL.

“I think it’s an opinion based on limited data,” Echemendia said about the conclusion by scientists at Boston University’s Center for the Study of Traumatic Encephalopathy that hits to the head suffered in hockey might lead to CTE. “My perspective is, we should not make wholesale changes until we have more than opinion and speculation.”

Some independent experts, however, say ample evidence exists.

“We in science can dot the line between blows to the head, brain degeneration and all of these other issues,” said Dr. Charles H. Tator, a neurosurgeon and researcher at Toronto Western Hospital who directs programs to reduce head and spinal-cord injuries in sports. “So in my view, it’s time for the leagues to acknowledge this serious issue and take steps to reduce blows to the brain.” Those steps, he said, included “getting fighting out of the game.”

Over the last two seasons, the NHL has banned most checks to the head and stiffened penalties for those and other rule violations through its new department of player safety. Those steps were taken primarily out of concerns for players’ health, to reduce concussions.

The NHL’s data from last season indicated that 8 percent of concussions resulted from fights. Still, Bettman said the league and the players are not inclined to enact measures that would limit fighting.

Tator said he believed fighting caused 10 percent of all concussions in hockey — “a significant number.” Asked if he could reduce by 10 percent a serious health problem by taking a particular step, he said, “Absolutely — the fighting issue is an important aspect of the whole issue of hits to the head.”

Dr. Jeffrey Kutcher, a neurologist who heads the University of Michigan NeuroSport program and is an NHL Players’ Association consultant to the concussion working group, said the elimination of fighting was a policy decision for the league and the players union to make, in much the same way cracking down on checks to the head was.

“I’m going to beg off on commenting on the policy part of it,” Kutcher said. “I can see the inconsistency that you’re outlining there.

“In essence, I would say there’s no more evidence that fighting is bad for the brain than there is that hits to the head are bad for the brain. The amount of evidence is the same — essentially, very little. Yet the decision was made on a policy level, let’s take head shots out of the game. There’s no more evidence, or less, for head shots than there is for fighting.”

Researchers generally agree that there is a link between repeated blows to the head and CTE. But they are uncertain which specific hits lead to the disease, and whether some people have a genetic predisposition. In Boogaard’s case, the Boston University researchers said it was impossible to know whether the condition was caused by blows he suffered in fights.

Dr. Michael J. Stuart, an orthopedic surgeon at the Mayo Clinic in Rochester, Minn., and chief medical officer for USA Hockey, acknowledged the range of opinions among medical experts.

“These are opinions, very educated opinions and very experienced people providing their opinions,” said Stuart, who was a chairman of last year’s Ice Hockey Summit: Action on Concussion at the Mayo Clinic.

Stuart said he applauded the NHL’s efforts to reduce the number of checks to the head. But “maybe they’re not ready to eliminate fighting now — I don’t know, but I certainly would hope that we head toward that to minimize risk,” he said.

“If we truly want to make every effort to reduce the risk of concussion in the sport of ice hockey we should eliminate fighting,” Stuart added. “There’s no doubt about that.”

The NHL finds itself in a position somewhat similar to that of the National Football League several years ago, when researchers began diagnosing CTE in the brains of former professional football players. NFL officials and the league’s medical experts initially dismissed the findings. But as more cases surfaced and congressional inquiries were conducted, the league was forced to make rules changes.

Dr. Michael Cusimano, a neurosurgeon at St. Michael’s Hospital in Toronto who is involved in efforts to reduce sports injuries, criticized the NHL for saying it needed more data.

“We heard this about 40 years ago with cigarette smoking,” Cusimano said. “Sure, there can be more evidence, but there’s some evidence out there that fighting is clearly a cause of brain injuries.

“What’s the threshold of evidence that Gary Bettman needs to see this?”