Controversy in the NFL over the risks of traumatic head injuries is reaching new heights today as one of the youngest promising players, 24-year-old 49er Chris Borland, has announced he's stepping away from the game over injury fears. Borland was considered "one of the top rookies in the N.F.L. last season" as the New York Times reports, and his announcement follows on two others by young players who are citing the same safety concerns for early retirement.

Borland told ESPN last night, "I just honestly 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." Borland has not suffered any recent major injuries, but says he's had two diagnosed concussions, one in high school playing soccer, and one during college football at the University of Wisconsin.

After more than 70 retired players have been diagnosed in recent years with varying degrees of memory loss, brain damage, and depression, Borland and some of his younger peers in the sport no longer want to wait until they show any symptoms.

"I feel largely the same, as sharp as I've ever been. For me, it's wanting to be proactive," Borland said. "I just want to live a long, healthy life, and I don't want to have any neurological diseases or die younger than I would otherwise."

Borland's decision follows on 30-year-old fellow linebacker Patrick Willis' decision to retire from the Niners, though he had cited his battered feet as the biggest cause.

Borland is the first to be so explicit about fearing head injury at such a young age, and the announcement is already sending ripples through the sport, with many players supporting his decision. You can see St. Louis Rams' Chris Long's tweets about Borland below.

Earlier this year, the Berkeley Repertory Theater premiered a new play, called X's and O's, that SFist reviewed here, which used the real life accounts of former NFL players and their families to talk about the problem of traumatic brain injury, and to question whether it will be the ultimate undoing of America's favorite sport.

Commentator Will Leitch is sounding alarm bells for the league, saying that the NFL has a serious existential problem on its hands, and it will certainly see a drop in players coming from educated, middle class families as time goes on. He notes that the NFL seemed to respond immediately to Borland's retirement only by seeing it as a problem of scouting, and how the 49ers could face trouble finding a good linebacker given renewed fears among young players.

"The response is not to change the game itself," he writes, "The response is to find people who do not understand that the game needs to be changed. It sees players — humans — as churn … as short-term investments, solely. It is pretending that everything is fine because the money is flowing so freely."