The death of former San Diego Chargers linebacker Junior Seau has again put the spotlight on the possibility of a link between concussions and depression so severe it drives professional athletes to take their lives.
Seau's death on Wednesday from a gunshot wound to the chest in an apparent suicide will sound all too familiar to shaken fans of the National Football League (NFL).
Last month, former Atlanta defensive back Ray Easterling, a plaintiff in concussion-related lawsuits against the NFL, died of an apparent suicide as did Chicago safety Dave Duerson, who shot himself in the chest last year and left a note asking his family to donate his brain to the NFL brain bank for study.
Even the National Hockey League (NHL) and their fans have wrestled with similar tragedies as tough guys Rick Rypien, Derek Boogaard and Wade Belak all died last offseason.
On the surface, their three deaths appear eerily similar as they all made a living on the unforgiving fringes of the sport, NHL enforcers who earned pay cheques by dispensing punishment on opposing players.
The three deaths in four months brought uncomfortable questions as to whether the events were a tragic coincidence or a sign of a deadly problem.
Now the NFL, the players and their lawyers are asking the same tough questions.
Alarm bells have been ringing in the NFL for several years as battered players stepped forward with tales of dementia and memory loss they believe to be the result of repeated blows to their heads during long careers.
According to NFLConcussionLitigation.com, 61 concussion-related lawsuits have been filed against the league by dozens of players, who allege the league negligently misled them about the dangers of concussions and other head injuries.
A report by Centers for Disease Control and Prevention estimates that as many as 3.8 million athletes suffer a concussion each year in the United States.
"Depression & suicide are serious matters and we as current and former NFL players should demand better treatment. Lack of info ... no more!!!," former Dallas Cowboys Hall of Fame running back Emmitt Smith said on his Twitter account.
"And for you current players who think this issue doesn't effect u. Get your head out of your but. Where u r 2day was his (Seau's) yesterday."
Seau spent 20 seasons in the NFL terrorising running backs and receivers but there is, so far, no proof that his death can be linked to chronic traumatic encephalopathy (CTE), a degenerative brain disease caused by repeated blows to the head which can only be diagnosed after death.
There is, however, mounting evidence that many professional football and hockey players suffered from CTE in their careers.
Duerson's brain, examined by Boston University's Center for the Study of Traumatic Encephalopathy found "indisputable" evidence of CTE in the tissue.
"NFL players often experience post-concussion syndrome," said James Johnston Jr., M.D., assistant professor of Neurosurgery at the University of Alabama at Birmingham in a statement. "They have a higher rate of depression, substance abuse, and dementia compared to the general population - it's thought this is connected to head impacts."
(Reporting by Steve Keating in Toronto; Editing by Frank Pingue)