'In 2015, there were 19 players 31 years old or younger who retired from the NFL, including 24-year-old Packers wide receiver Adrian Coxson, 25-year-old 49ers offensive lineman Anthony Davis and 24-year-old 49ers linebacker Chris Borland, and 26-year-old Titans quarterback Jake Locker. All cited concerns about concussions, though Davis has now reconsidered and wants to return to play.'