21. Bo Jackson – Retired at 28 in 1990
Calling Vincent “Bo” Jackson a “superstar” is an understatement. Bo wasn’t just an freak athlete — he was skilled enough to be named an All Star in two different professional sports. Because of his on-field success and off-the-field endorsements, including the wildly successful “Bo Knows” marketing campaign by Nike, he became a cultural phenomenon.
Shortly after the 1990 season — a year where he hit more than 20 home runs for the Kansas City Royals, and was named to the Pro Bowl — Jackson dislocated his hip while playing in the Raiders opening playoff game in January of 1991.
Jackson stated that he popped his hip back into the socket after the run, which actually damaged the blood vessels going to his hip. Shortly after that, he was diagnosed with avascular necrosis of the hip joint, forcing him to retire from football. Sadly, Jackson only played 38 games in four NFL seasons.