For every year of absorbing the pounding and repeated head collisions that come with playing American tackle football, a person’s risk of developing chronic traumatic encephalopathy (CTE), a devastating neurodegenerative disease, increases by 30 percent. And for every 2.6 years of play, the risk of developing CTE doubles. These new findings from an analysis of 266 deceased former amateur and professional football players—reported in Annals of Neurology by a team of researchers from the Boston University CTE Center—are the first to quantify the strength of the link between playing tackle football and developing CTE.