After 2011, we’ll never be able to look at violent sports like football or ice hockey the same again. That’s because this year saw the release of study after study connecting repeated head collisions and concussions in athletes to the risk of brain damage down the line. Perhaps no single player better symbolized that connection than Derek Boogaard, a fearsome National Hockey League enforcer who committed suicide in 2011 after suffering years of concussions in hockey fights. Autopsies done on the 28-year-old Boogaard — the subject of a magisterial series in the New York Times — showed that he had the kind of brain damage usually seen in dementia patients at the end of life. Both football and hockey moved to improve player protection and penalize head hits, but the damage is far from over.