Substantiating the claims with medical records can also prove difficult. In Victoria, where most A.F.L. teams play, doctors are required to keep records for only seven years after a patient turns 25. This makes it difficult for older players to document their injuries.

“We’re reaching back 20, 30 years,” Anderson said.

While they plot a legal strategy, some former players are pledging their brains to the country’s only sports-specific brain bank so future generations can learn from their misfortune. Michael Buckland, a neuropathologist in Sydney, spent years looking at the brains of people with multiple sclerosis and other diseases before he read about chronic traumatic encephalopathy, or C.T.E., the degenerative brain disease found in athletes who played collision sports that can only be diagnosed after death.

“To me, it looked like a new pathology they were describing, so I was hoping to see if we could find it in Australia,” said Buckland, who opened the brain bank last year.

Not surprisingly, the A.F.L. has not offered to help finance Buckland’s research, but he did not expect other scientists to criticize his work by suggesting that there is no hard evidence that head injuries can lead to C.T.E.

“I don’t think I really knew what I was getting myself into,” Buckland said. “Some people are clearly unhappy about it.”

Buckland’s first diagnosis, of a 77-year-old former Australian rules football player with dementia, was negative for C.T.E. In June, he was involved in research that showed two rugby players were found with C.T.E. The diagnoses, which were done by a different department at Buckland’s hospital, shook the rugby world. A fourth diagnosis, of an ex-boxer who committed suicide, was also positive for C.T.E.

Buckland said that in the years ahead, more diagnoses are sure to come back positive.

“It’s got to be here, given the sports we play in Australia,” Buckland said.