Since then, one other Division I conference has copied the Ivies. Some have made other rules changes, and started long-term research projects on head trauma in athletes. Bolstered by the new rules, advocacy groups like All Players United, increased news media attention to head trauma in the National Football League, and the deaths of football players who suffered from head trauma, calls for action in the sport whose revenue helps keep college athletic departments afloat have become impossible to ignore.

But as researchers and policy makers know, concussions aren't only a danger in football -- in fact, football isn't even the sport in which they present the greatest risk, at least in terms of frequency.