Owen Thomas wasn't an NFL superstar. He didn't even play for a big U.S. college team. But months after his passing, the way the young defensive lineman died is raising questions about the sport's very future.

The 21-year-old Thomas, who played for the University of Pennsylvania, hung himself in April, just a couple of weeks after being named a team captain.

His suicide shocked his family, who say he showed no signs of depression before his death. There was further shock when an autopsy revealed that Thomas had died with signs of a brain disease called chronic traumatic encephalopathy.

CTE is a condition caused by repeated hits to the head and concussions. It can cause behavioural changes, including erratic behaviour, dementia, depression and, occasionally, suicide. Doctors who examined Thomas's brain say he showed mild -- but definite --signs of the condition.

Questions about the long-term effects of blows to the head are nothing new to sport. Indeed, CTE is also called dementia pugilistica, or "punch-drunk syndrome," a term to describe the behavioural changes seen in many boxers later in life. It's suspected that the dementia that afflicted countless boxers, including Floyd Patterson, Sugar Ray Robinson and Joe Louis, derived from "punch-drunk syndrome."

In recent years, researchers have zeroed in on the distinct brain markings of CTE in former NFL players. They've found it in more than 20 deceased players. Recently, autopsies on former Philadelphia Eagle Andre Waters, who committed suicide, and Chris Henry, who died after falling off the back of a truck during a domestic dispute, also revealed CTE.

Mike Webster, a legendary centre for the Pittsburgh Steelers, suffered for years from amnesia, dementia and depression. The Hall of Famer ended up homeless and died at the age of 50. He too was diagnosed with CTE after his death.

Last year, Reggie Fleming, a hard-nosed NHLer from the 1960s and '70s became the first hockey player diagnosed with CTE. His son told The New York Times that his father had struggled with emotional problems following his retirement.

What makes Thomas' death and diagnosis so disturbing is that unlike former players like Webster and Fleming, Thomas was so very young, raising questions about how early the condition can develop.

Dr. Charles Tator, a University of Toronto professor of neurosurgery, who has long researched brain and spinal trauma, says it's only recently that doctors have begun to take seriously the long-term effects of concussions.

"During my early career, a concussion was felt to be quite innocent. In fact, we used all kinds of words to describe them, like 'dings' and 'bell-ringers.' But in, oh, the last 10 years I would say, doctors are starting to think of concussions as brain injuries," he told CTV.ca.

Tator says many questions about concussions still need to be answered, most notably: how do repeated head blows turn into a degenerative brain disease like CTE?

"That is the question. Nobody knows the answer to that question. And that's why it's important for researchers to study this carefully, and that's why the Boston group has jumped on this very aggressively," he says.

Tator is referring to the Center for the Study of Traumatic Encephalopathy, created in 2008 by Boston University researchers and the Sports Legacy Institute. They've been examining the brains of former athletes, including NFL players, to better understand CTE.

What's interesting with Owen Thomas is that although he had played football since grade school, his family says he was never once diagnosed with a concussion.

That raises even more troubling questions: Is it possible that even head trauma milder than a concussion could lead to CTE? Or was Thomas actually being concussed and feeling pressured to ignore the signs?

TSN commentator Matt Dunigan knows well the pressures football players place on themselves. The former CFL quarterback suffered 12 documented concussions through his 14 years with the league. The end finally came when he suffered four big hits in one game.

Dunigan tells CTV.ca he knew after the first two hits that his career was over. And yet he went back on the field for another series, sustaining two more hits that finally "drove the nail in the coffin."

He says players at the college and professional level are highly competitive athletes who don't want to have to stop playing.

"As an athlete or a competitor, that's what you do for a living. You get to the point where you perform at a level of excellence, physically and mentally. You're working your tail off to keep your body as its highest possible level and you try to ride that out as long as possible," he says, in his well-known Texas drawl.

Today, more than a decade after that last game, Dunigan still lives with memory loss, headaches and other effects from all those hits to his head.

"The ability to speak properly is an ongoing challenge for me. To this day, 14 years later, I still deal with post-concussion syndrome and its effects. And that is why working for TSN has been such a blessing. It's great medicine; it forces me to be concise, precise and clear with my thoughts," he says.

Dunigan says that when he retired in 1996, there was awareness of concussions, but no guidelines or protocols for returning to play. He says he is heartened to see the NFL making changes in the last year and finally taking concussions seriously.

"I think the game is taking steps in the right direction. The medical field and those involved in all levels of the sport are starting to understand this and take it seriously and move in the right direction, which is good for everybody," he says.

Others are less optimistic.

Former Chicago Bears safety Matt Bowen recently wrote a column in the Chicago Tribune to say that as a now-retired, 35-year-old father, his football legacy of daily crushing headaches makes him question whether his seven years in the NFL were worth it.

He suggested players have far too much at stake to admit to concussions and risk being sidelined for weeks.

"Without the guaranteed contracts we see in Major League Baseball or the NBA, NFL players will continue to sacrifice their health and their future by playing through concussions," he wrote.

"No one wants to sit out and no one wants to become a ghost — that player who can't practise or can't play, who is tucked away in the training room while someone else is out there on that field stealing your money and your future."

Other football columnists worry that as the light begins to shine on how dangerous football concussions can be to young players, the very fate of the game could be in jeopardy.

"If the NFL, NCAA, and other football bodies do not take serious action right now to combat the constant, destructive head trauma that is as much a football staple as the extra point, the sport could face a massive decline in popularity and relevance over the next 20 to 30 years," wrote The Atlantic sports columnist Jake Simpson earlier this week.

As for Owen Thomas, his death is already bringing about changes for younger football players. This week, his mother, the Rev. Kathy Brearley, testified before a U.S. House committee that's drafting legislation to require high schools to develop plans for concussion safety and management and increase student and parent awareness of their dangers.