On August 19, 2012, in week two of the NFL preseason, Indianapolis Colts wide receiver Austin Collie ran 17 yards out from the line of scrimmage, cut right toward the center of the field, caught a pass, and was immediately tackled by Pittsburgh Steelers cornerback Ike Taylor. As Taylor came in for the hit, his helmet appeared to glance off the left side of Collie’s helmet. Then the cornerback wrapped his arm around Collie’s neck and jerked the receiver’s head to the right. An instant later, Steelers linebacker Larry Foote came barreling in from the opposite side and slammed his elbow into the right side of Collie’s helmet. As the receiver fell to the ground, his helmet first hit Foote’s knee and then struck the ground face-first.

Collie sat up, dazed, and had to be helped off the field a minute later. He didn’t return to play for three weeks. The diagnosis: concussion. It wasn’t the first time Collie had suffered what’s clinically called a traumatic brain injury. On November 7, 2010, he spent nearly 10 minutes lying motionless on the 34-yard line after being hit in the head almost simultaneously by two Philadelphia Eagles players. Medics carried him off the field on a stretcher. In his first game back, two weeks later, he left in the first quarter with another concussion. He missed three more games, only to suffer yet another concussion on December 19, which ended his season.

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.