According to the Concussion Legacy Foundation, CTE is typically caused by repeated hits to the head — in many cases, this means hundreds or thousands of traumas — over the course of a person's life. While CTE is often associated with concussions, smaller hits may collectively be even more damageing. Full-contact sports are the biggest culprits. Football, wrestling, and boxing are the most obvious, but other sports — such as hockey, football, and rugby — have been linked with CTE as well. And it's not just athletes: military vets who were exposed to repeated explosions or otherwise injured in combat have also been diagnosed with CTE.