Rex Grossman
Grossman had a sensational college career at Florida and looked like he could become a franchise quarterback in the NFL. However, after serving as a backup as a rookie, injuries prevented him from establishing himself as the full-time starter for the Bears for the next two seasons. In 2006, he finally managed to start all 16 games, and despite nearly throwing as many interceptions as touchdowns, Grossman played well enough to guide the Bears to the Super Bowl, ultimately losing to Peyton Manning and the Colts.
However, early in the 2007 season, Grossman lost his starting job to Brian Griese. He didn’t get back to being a full-time starter again until he started 13 games for the 5-11 Redskins. Despite remaining in the league as a backup and practice squad player until 2015, Grossman never threw a pass after the 2011 campaign and never had any kind of sustained success outside of that 2006 Super Bowl season.