Kurt Warner
Nobody had a career like Warner’s after he belied his undrafted status to become a Super Bowl MVP. But arguably the quarterback held on for too long to his NFL dream. He was brilliant for the Rams before his form fell apart. Then he found himself in Arizona and had a career renaissance.
He helped the team to a Super Bowl appearance but they failed to win. Retirement beckoned for the signal-caller but he chose to play for another season. Hindsight is a wonderful thing but this was a mistake. In the end, he retired after the Saints took a bounty out on him (via The Guardian).