It was one thing when Chris Borland, a rising NFL rookie who hadn't yet ingratiated himself to San Francisco 49ers fans or the rest of the NFL-viewing public, decided to call it quits on his professional football career far earlier than expected. Sure, Borland played well during that initial season, collecting 108 tackles and 2 interceptions, but he wasn't a bonafide star. He may well have become one, but surely his concerns over the lasting impact of the trauma he would suffer as a fulltime NFL player were singular, were simply a product of his own experience.

But when Niners star Patrick Willis decided to retire? And then Marshawn Lynch? And Jerod Mayo? And Calvin Johnson? And Husain Abdullah?

A troubling trend seemed to be emerging in the NFL - stars calling it a career long before it seemed they'd reached their actual athletic expiration date. It left fans flustered and concerned, but ultimately unworried. Surely it wasn't just an strange spate of retirements all coming at the same time. The connection to the growing concerns over concussions, chronic traumatic encephalopathy (CTE), and other injuries was tenuous at best, right?

Maybe not.

Borland, as part of a panel discussing the documentary "Requiem For A Running Back," said that he believes the trend of early retirements from the NFL will only continue, especially as our understanding of CTE grows.

"I think historically, Jim Brown and Barry Sanders are viewed as early retirements," Borland said. "I think whenever a guy decides to walk away is when he and his family decides he's not going to play a game anymore. And even if you play for 20 years and are a Hall-of-Famer, you still have a life to live after football. So I think that's always been a cliché, but that's starting to get real, tangible results."

Of course, the NFL has done its best to slow the steady groundswell of fear over the long-term effects of concussions on its players. A recent New York Times report alleging that the NFL skewed concussion data was met with a firm and vehement response, and when an NFL executive admitted during a congressional roundtable that a link does exist between football and CTE, two of the league's most high-profile owners, Jerry Jones and Jim Irsay, did their best to laugh off the mounting evidence.

Borland went on to note that a player like former Iowa Hawkeyes standout and New York Giants safety Tyler Sash had high levels of CTE in his brain, despite having played the game professionally for only two years. Sash died last year after overdosing on painkillers.

"To see a guy who's probably taken less hits to the head than me to have a stage of CTE similar to Junior Seau was eye-opening," Borland said.

At this point, Borland has moved on from the NFL, but he remains interested in learning more about mental health and the impact of head trauma on the human brain. He still holds the game in high regard, but he fears the fundamental nature of a sport that's built on constant, violent collisions.

"It could be the greatest game in the world, but simultaneously maybe the worst," Borland said. "And the crux of the issue for me, I think, is that what makes it so great is also what makes it detrimental and scary and everything, the violence. So I don't regret my decision. Miss the game, but that time was going to come at a certain point anyway, so moved on with my life."