San Francisco 49ers linebacker Chris Borland has become the latest player to retire prematurely from the NFL.
The talented rookie joins recent retirees Patrick Willis, Jason Worlids and Jake Locker - three other NFL starters whose careers were ruined by injury.
Willis is 30, Locker is 26, Worlids 27. Borland is just 24. These are players at or approaching their peaks, voluntarily walking away from tens of millions of dollars.
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This should scare the NFL, an organisation that has been accused of failing to look out for the players that put their bodies on the line week in, week out for The Shield.
The message it sends to parents of children involved in the sport is stark, and without a flourishing grassroots, its long-term viability is limited.
Willis, an All-Pro star, retired due to a lingering foot injury. Worlids just walked away. Locker did the same after injuries extinguished any 'burning desire' he once had for the game.
But it's Borland's announcement last night that will have league officials most worried.
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The University of Wisconsin standout has had two diagnosed concussions in his life, but thinks he played through one during training camp last year in desperation to make the team.
That made him question his commitment to a sport that routinely asks its players to test the limit of punishment a human body can take.
Speaking to ESPN's Outside The Lines, Borland said: "I just want to do what's best for my health.
"From what I've researched and what I've experienced, I don't think it's worth the risk."
The decision, taken after consultation with medical experts, friends and family, means Borland becomes the most high profile NFL player to walk away from the sport over concussion fears.
His peers were split on the decision itself, but united in their support.
It's a topic that is not going away for the NFL. In fact, looking at the furore in this year's edition of the rugby Six Nations, another bruising contact sport where head collisions are common, it's only likely to turn the volume of the conversation up.
Then there's Sidney Rice, the former-Seahawks receiver who quit the game last year after his team won the Super Bowl. He retired age 27.
He said this week: "You have these guys that have been going to the same house for 25 years. And all of the sudden they get to a certain point on their way home and they have to call their wives to get the directions home. So that is something that really hit home for me after having experienced so many concussions," said Rice.
NFL careers are brutally short, the NY Times reports that 75 per cent of drafted players are either cut or retired within four years.
That's a shockingly high number, but it becomes more worrying for the NFL when players are retiring because of the potential risk of injury.
Until now, players have signed contracts and taken the risks willingly. Now a player has given up those contracts because he calculates the risk is too great.
As Maurice Clarett, who had his own run in with the NFL over draft eligibility rules, pointed out, players like Borland can take such decisions when they feel confident in the alternatives available to them.
For many college athletes and professionals, who grew up in poverty and battled every day to earn that first big pro pay check, there's no other option but football.
The NFL is now in a vulnerable position, largely thanks to its own mishandling of the concussion issue. Last July, a class action suit brought against the league resulted in an approved settlement, compensating thousands of former players for concussion-related injuries.
An initial $765m settlement reached in 2013 was later revised, and the cap on compensation of affected players removed. Allegations of league interference with an Outside The Lines documentary also attracted negative publicity.
Small steps towards a larger change in player safety now feels inevitable.
The NFL, a billion dollar industry, has the popularity, and most importantly the money, to blindly trudge forward through these controversies.
But revolution has a habit of creeping up on you.