GREENWICH — By 1996, when he was playing for the Buffalo Sabres, hockey player Pat LaFontaine had had six documented concussions, not counting the stick that hit him in the face and broke his jaw.

Later in the season, when 6-foot 6-inch François Leroux of the Pittsburgh Penguins dealt LaFontaine a brutal blow, LaFontaine’s helmet popped off and his forehead slapped the ice.

That was the beginning of a dark spiral for LaFontaine. He knew something was wrong, but doctors and trainers, who had less understanding of concussions at the time, allowed him back on the ice.

LaFontaine didn’t feel like himself. In his last game of the season against the Philadelphia Flyers, the rink was spinning in his vision. LaFontaine was terrified.

His coach pulled him off the ice, and he was flown to a hospital in New York.

“I was a shell of myself, but I was told at the time that I was OK,” LaFontaine told an audience at the Nantucket Project Library in Greenwich Tuesday night.

Doctors did warn him that another major hit could cause serious brain issues. And in 1998, playing for the New York Rangers, LaFontaine was dealt that blow, when he collided with a teammate.

His 15-year professional hockey career was over. But his struggles with head trauma were not.

LaFontaine sunk into a deep depression due to post-concussion syndrome. He remembers barely being able to shower or leave the house. One day, when he laughed on the phone with his wife, she cried: It was the first time he had laughed in three or four months, she said.

As LaFontaine, now 52 and a National Hockey League Hall of Fame inductee, shared his story, Chris Nowinski, founder of the Concussion Legacy Foundation, nodded along.

Nowinksi, 39, knew LaFontaine’s pain. He, too, had experienced the trauma of repeated blows to the head, concussions, and post-concussion syndrome. His head still aches some days, Tuesday night included, he said.

Nowinski played college football for Harvard University and he joined the professional wrestling company World Wresting Entertainment after graduation. Called “Chris Harvard” in the ring, Nowinski suffered a damaging blow during a match in 2003. He blacked out in the ring, but when he came to, he insisted on finishing the match despite his throbbing head.

He lied about his pain for the next five weeks, even though nausea prevented him from finishing his work-outs. When he sleepwalked in a hotel room in Indianapolis and jumped through a nightstand, Nowinski finally got help.

“I just never got better,” he said. “One of the horrible things about post-concussion syndrome is sometimes you get better and sometimes you really don’t.”

In October 2006, Nowinski self-published a book, “Head Games: Football’s Concussion Crisis,” which details his career-ending injury and discusses the dangers of concussions in football and other contact sports. The book didn’t make many waves at the time though, Nowinski said.

Later that year, when Andre Waters, a 44-year-old NFL defenseman shot himself dead, Nowinski called Waters’s mother. He asked her to donate pieces her son’s brain to be studied. A pathologist found Water’s brain tissue resembled that of an 85-year-old man suffering from early stages of Alzheimer’s disease.

The episode made Nowinski angry; he wanted people to stop ignoring the dangers of repeated head injuries.

He got a doctorate in behavioral neuroscience from Harvard, launched the Sports Legacy Institute (now known as the Concussion Legacy Foundation) and in partnership with Boston University School of Medicine, formed the Center for the Study of Traumatic Encephalopathy (CTE Center) in 2008.

The CTE Center is now a leader in the study of the neurodegenerative disease chronic traumatic encephalopathy, which leads to behavioral and mood problems and eventually dementia in people who suffer repeated head injuries.

Of 111 brains of deceased NFL players donated to and studied by the CTE Center, 110 were found to have CTE, Nowinski said.

“We opened up Pandora’s Box here and it is scary what we found,” Nowinski said.

Now, both Nowinski and LaFontaine are focused on changing youth sports.

The Concussion Legacy Foundation has launched a campaign to promote flag football for youth under 14 years old. It also campaigned to eliminate “headers” in soccer before 11 years old.

“We are trying to create a culture where we actually stop hitting people in the head so much,” Nowinski said. “We are really focused on kids. Now that I know what I know, I can’t believe that we subject people to purposeful hits to the head in sports.”

Meanwhile, LaFontaine, who now works for the National Hockey League, shared how he has been helping the NHL partner with hockey leagues throughout the U.S. and Canada to change the sport. The league has developed a declaration of principles that aims to provide a fun, age-appropriate hockey experience to youth, lessening focus on winning and elite teams.

“We’ve lost ourselves a little bit in sports,” he said. “At the end of the day, it is truly about creating the best possible, positive family environment.”

LaFontaine serves on the NHL’s concussion subcommittee. The NHL has worked to reduce hits to the head for player safety, he said.

“The head is really off limits,” he said.

emunson@greenwichtime.com; Twitter: @emiliemunson