CTE is not guaranteed to anyone who plays football, it has been proven to hinge on 1st whether you are predisposed & 2nd repeated subconcussive hits to the head. "Severity of the disease is categorized into four stages, with stage 4 being the most severe. While researchers don't know exactly why certain people develop the disease and others don't, they believe that it results from repeated blows to the head that trigger a build up of tau proteins in the brain. Could veterans have concussion-related CTE? CTE has been called football's "concussion crisis," however experts point out that CTE can develop from any repeated head injury. According to the Boston University CTE Center, "this trauma includes both concussions that cause symptoms and subconcussive hits to the head that cause no symptoms." These subconcussive hits can include the repeated trauma the brain experiences from constant plays, hitting the turf, and tackling. Wrestlers, boxers, and military troops have also been diagnosed with the disease."