Sport: Football, baseball
Age retired: 28 (football), 31 (baseball)
Years as a pro: 4 (football), 8 (baseball)
One thing to know: Considered one of the best athletes of all-time, Jackson managed to play two sports at once, playing football with the Oakland Raiders when the MLB season ended. Jackson suffered a career-ending hip injury in the 1990 NFL season, then returned to baseball to play two more years, but was not the same player. He retired for good in 1994.