6. Doug Williams
Doug Williams was a pioneer in the NFL, becoming the first African-American quarterback to win the Super Bowl in the history of the league. But the rest of his NFL career wasn’t nearly as noteworthy as that one accomplishment. Williams had a promising start to his career in Tampa Bay, taking the perennially-awful Buccaneers to the playoffs three times in four years, including the NFC Championship game in 1979. But after leaving Tampa because of a contract dispute, he played in the USFL, and then joined the Washington Redskins as a backup.
After coming off the bench and replacing the injured Jay Schroeder en route to the victory in Super Bowl XXII, Williams was plagued by injuries and eventually replaced by Mark Rypien. Two years after winning the Super Bowl, Williams retired.