FILE - In this Thursday, Nov. 9, 2017 file photo, Ann McKee, director Boston University's center for research into the degenerative brain disease chronic traumatic encephalopathy, or CTE, addresses an audience on the school's campus about the study of NFL football player Aaron Hernandez's brain, projected on a screen behind in Boston. According to a new public service announcement, signing a pre-teen child up for tackle football is like teaching him to smoke. The ad from the Concussion Legacy Foundation encourages parents to choose flag football for children younger than 14. (AP Photo/Steven Senne, File)