EAST RUTHERFORD, NJ – SEPTEMBER 13: Quarterback Johnny Manziel #2 of the Cleveland Browns hits the ground after being hit by Buster Skrine #41 of the New York Jets during a game at MetLife Stadium on September 13, 2015 in East Rutherford, New Jersey. The Jets won 31-10.(Photo by Rich Schultz /Getty Images)

Source: The Long-Term Effects of Concussions on NFL Players – Forbes