And the NFL probably feels like it could use a good party to put 2012 behind it. It was a year that brought to light the New Orleans Saints bounty scandal ... in which the team paid players bonuses for deliberately injuring opposing players. 

And it was a year in which a class action lawsuit was brought against the NFL by thousands of former football players who are seeking damages for the brain injuries they suffered on the job. 

Most shockingly, it was a year in which Kansas City Chiefs player Jovan Belcher murdered his girlfriend, drove to the stadium, said thanks to his coach, and then killed himself. 

And a year in which a future Hall-of-Famer, Junior Seau killed himself with a gunshot to the chest. He chose the chest because he wanted his brain intact, so it could be studied for signs of injuries he sustained as a player -- injuries that led to the mental illness and anguish that made his life unbearable. 

In the NHL, it's "post-concussion syndrome" that sidelined big stars like Sydney Crosby, that dominated the headlines. But something more insidious has been troubling doctors and neuroscientists. The suicides of hockey tough guys like Rick Rypien and Wade Belak, along with the death of Derek Boogaard, have been linked to a career of blows to the head. 

Boogaard's brain, like those of renowned enforcers Bob Probert and Reggie Fleming, was found to have chronic traumatic encephalopathy, or CTE. It's a condition that can destroy or end lives ... either by violence or long, slow decline.

It's why some neuroscientists and doctors want fighting to be banned in hockey. It's why the NFL has a crisis on its hands. And given what we know now about the effects of being knocked in the head repeatedly, it's enough to raise the question of whether sports fans are morally culpable in the lives of athletes being ruined or cut short. 

Malcolm Gladwell (above) is one of the more prominent people raising that question. He's the best-selling author of The Tipping Point, Blink and Outliers, and he's a long-time staff writer with The New Yorker magazine.