High school athlete Graham Hill, number 50, suffered a concussion in 2013 while playing football at Trinity Christian Academy in Addison, Texas. Courtesy of Jeffrey McWhorter hide caption

itoggle caption Courtesy of Jeffrey McWhorter

Making and taking a hit chest to chest, instead of skull to skull, is easier to remember if you're not wearing a helmet, say University of New Hampshire Wildcat football players. Jack Rodolico/New Hampshire Public Radio hide caption

itoggle caption Jack Rodolico/New Hampshire Public Radio

Junior Seau sustained many concussions during his career and was suffering from a degenerative brain disease when he killed himself in May 2012. Otto Greule Jr./Getty Images hide caption

itoggle caption Otto Greule Jr./Getty Images