San Francisco 49ers linebacker Chris Borland had a promising football career in front of him. He is 24 and set to take over the starting position vacated by the retiring Patrick Willis. Borland had a standout rookie season, garnering 108 tackles although he only hit the starting lineup in Week 7. He was named the NFL's Defensive Rookie of the Week in Weeks 10 and 11, and then Defensive Rookie of the Month. He was on track for all the riches and fame of a long NFL career, and then he announced his retirement. He cited fear of head trauma, and a concern for his future health.

This decision will send shock waves through NFL player ranks. I don't think it will lead to an immediate widespread spate of retirements -- but it clearly will make players think about whether the allure of the NFL is worth the risk of future dementia. I had a crisis of conscience in the 90s watching clients get hit in the head. We held a concussion conference with leading neurologists that had many top players listening to the facts. One of those players is now suffering from early signs of dementia. We issued a white paper with a variety of suggested changes. Not much happened.

In 2005 Warren Moon, the Concussion Institute and I held a conference at which neurologists like Bennet Omalu, Julian Bailes, Robert Cantu, Kevin Guskiewicz and others suggested that three or more concussions could occasion an exponentially higher rate of ALS, Alzheimers, premature senility, chronic traumatic encepalopathy and depression. I called it a ticking time bomb and un-diagnosed health epidemic that would get worse because of the size, strength and speed of athletes. The physics of some hits, the actual G-force, accelerated the risk.

I now believe that each time an offensive lineman hits a defensive lineman at the inception of every football play it creates a low level sub-concussive event. So an offensive lineman could play in high school, collegiate and professional ball sustaining as many as 10,000 sub-concussive blows, none of which were diagnosed or brought to the attention of the player. The aggregate of these hits would almost certainly be more destructive of brain health than three knockout blows.

If 50 percent of the mothers in this country understand these facts and tell their teenage sons "You can play any sport and we will support you, but NOT tackle football", it won't destroy football. It will change the socio-economics of those who plays. The same kids who now box to escape negative economic circumstances will be the players willing to accept the risk. I love football and think it brings great life lessons applicable to other callings. We need research into helmetry and nutraceuticals and pharmaceuticals that can prophylactically protect the brain or heal it after injury. Changes in the amount of contact are also helpful.

Pro athletes have all been in a state of denial about their physical health since learning these norms in Pop Warner and Little League. For Chris Borland, at the beginning of a promising career, to walk away from football is a dramatic marker.

His retirement is a clarion call to other players to assess their futures, and another sign that prevention and cure of concussion has to be urgently addressed.

-- Leigh Steinberg has represented many of the most successful athletes and coaches in football, basketball, baseball, hockey, boxing and golf, including the first overall pick in the NFL draft an unprecedented eight times, among more than 60 first-round selections. His clients have included Hall of Fame quarterbacks Steve Young, Troy Aikman and Warren Moon, and he served as the inspiration for the movie "Jerry Maguire." Follow him on Twitter @leighsteinberg.

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