On Wednesday, the longtime N.H.L. veteran Daniel Carcillo, now retired, announced that he would donate his brain, joining a growing list of hockey players that includes Hayley Wickenheiser and Andrea Ruggiero, Olympic gold medalists who made the pledge this year.
Parker made no plans for a brain donation before he died from an infection related to a catheter that treated pulmonary hypertension. The subject was raised with family members just moments before Parker was to be cremated in Minnesota.
“It’s hard to make the decision at the time because you’re grieving so hard,” John Parker said. “Once my mom gave the half-O.K., we made the call.”
The C.T.E. results, recently given to the family, confirmed suspicions.
“He was fighting through more than we knew, probably,” John Parker said. “More than we could see. And he was persevering the best way he could.”
Parker was a high school star in Minnesota, a national champion at Michigan State and a gritty professional who played all or parts of five seasons in the N.H.L., ending when he was knocked out with a hit in 1991 while playing for the Hartford Whalers. It was barely noted.
His athletic rise and eventual postcareer struggles followed a now-familiar arc among many later found to have had C.T.E. — relative fame and fortune fading into an erratic postcareer life overcome by symptoms associated with brain injuries.
“There was a change in that lighthearted kid who left White Bear Lake and the one who came back from the N.H.L.,” Scott Parker, Jeff’s older brother, said.
The Parkers, with three boys, were a quintessential hockey family in suburban Minneapolis-St. Paul — broken windows in the garage from pucks flying during indoor games, a pond across the road and rinks at the high school up the street.
“One of us would always come home with a bloody nose,” Scott Parker said. “Pretty typical of outdoor hockey in the ’70s, trying to earn your stripes.”
All three brothers played in college and won national championships — Scott at Wisconsin-Eau Claire, Jeff at Michigan State and John at Wisconsin. Jeff, the middle boy, was the best player. He grew to 6-foot-3 and about 200 pounds, and could shoot a puck over the net from past the blue line as a child, his brothers said.
Before he turned 18, Parker was drafted in 1982 by the N.H.L.’s Buffalo Sabres in the sixth round, No. 111 over all. He delayed a leap to the pros to play three seasons at Michigan State. He was a strong, aggressive forward, trusted to kill penalties and spent a lot of time in the penalty box himself.
Professional coaches immediately saw an additional role for Parker. At an early practice, awaiting a face-off, he was told to fight, his family said.
“I remember him calling my mom, and he was crying,” Scott Parker said. “He didn’t want to do that. He just wanted to be a hockey player. It was a role bestowed on him.”
The grainy highlights of his pro career are filled mostly with big hits and bare-knuckle fights. Hopes to come back after being knocked down for the last time did not last long.
“Once he started to work out a little bit, he told me, ‘Something’s wrong, I don’t think I can play,’ ” John Parker said. “He went from being, ‘I’m willing to fight, I’m willing to hit someone,’ to “I don’t want to get hit.’ And that wasn’t him.”
Parker’s brothers said he permanently lost his sense of smell and taste — everything tasted like burned toast, he would say. Trying to explain the persistent fog in his mind, he often said his head felt “oblong.”
Parker soon exhibited many of the symptoms now associated with C.T.E., such as memory loss and impulsivity. He struggled with bright light and spent countless hours in the dark, trying to soothe his brain. He tried to finish college, Scott Parker said, “but his brain couldn’t function like that anymore.” He could not read without headaches or keep a steady schedule. He would miss appointments or show up at the wrong place. He once came to a meeting without shoes.
He lost a lawsuit filed against the N.H.L., the Whalers and Capitals, and the arena where the last injury took place.
“By deciding to participate as a player in the hockey game, Parker voluntarily chose to accept the risk,” a judge wrote in a 1995 ruling.
Parker lost his savings and spent several years homeless around St. Paul. The family lost track of him in the late 1990s before he emerged again. He spent most of the final 15 years working odd jobs, mostly as a bartender.
Scott Parker said he spoke to Jeff on the phone about three times a week, and the conversations were mostly playbacks of stories that Jeff did not remember that he had told before.
One symptom associated with C.T.E. that he did not display, his family said, was wild mood swings or violent behavior. He did not ask for help or attention. He would always say that he was fine, and family and friends considered him affable and easygoing, to the end.
Parker was one of the more than 100 former N.H.L. players named as plaintiffs in a continuing class-action suit against the league, arguing that the N.H.L. concealed information from players about the risks and long-term effects of concussions. The family said Parker had no acrimony toward the N.H.L., but hoped awareness might aid future players.
That lawsuit has churned through United States District Court in Minneapolis for years. The sides now await a judge’s decision on whether it can continue as a class-action suit — which would automatically add about 5,000 plaintiffs to the case. A similar situation in the N.F.L. case in 2015 pressured the sides to reach a settlement.
In the lawsuit recently, the N.H.L. asked for records from the CTE Center’s brain research, including the names of all the athletes who donated or agreed to donate their brains. The judge denied the request last month.
The N.H.L. has long argued that it is impossible to directly link hockey and C.T.E., though an email chain from 2011 seemed to contradict that public stance. As recently as last month, Bettman reiterated his belief on a New York radio show that there is no medical evidence linking hockey and C.T.E.
In a recent interview with The Times, Bettman said that “the game is safer now than it ever has been,” citing evolution in things such as medical care and rule changes.
“I think there’s still a lot that people have to learn,” he said. “I get concerned when people scare players for no reason. And there have been instances of that, some of them tragic. I think people have to be very careful before jumping to conclusions.”
In an essay for The Players’ Tribune in April, the Hall of Fame hockey player and author Ken Dryden pleaded with Bettman to put an end to hits to the head in hockey. Dryden said his 2017 biography of Montador, a 10-year N.H.L. veteran who died in 2015 at age 35 and was found to have had C.T.E., was meant for an audience of one: Bettman.
The growing pressure has not moved the N.H.L. yet. Perhaps each new finding of C.T.E. nudges it closer to changing its mind.
“It’s an awful responsibility that the N.H.L. has,” said Scott Parker, who has coached a Minnesota high school team for 30 years. “If you’re going to let them bare-knuckle fight, then take care of them. Do the right thing. Take care of these kids. Give them some health care. Give them some dignity. Do they have to fight these things alone?”