Professional football players receive as many as 1,500 hits to the head in a single season, depending on their position. That's 15,000 in a 10-year playing career, not to mention any blows they received in college, high school, and peewee football. And those hits have consequences: concussions and, according to recent research, permanent brain damage. It's not just football, either. Hockey, lacrosse, and even sports like cycling and snowboarding are contributing to a growing epidemic of traumatic brain injuries. The CDC estimates that as many as 3.8 million sports-related concussions occur in the U.S. each year. That number includes not only professionals but amateurs of all levels, including children. Perhaps most troubling, the number isn't going down.