Chris Johnson
Johnson serves as a warning to GMs across the NFL landscape. He was arguably the second-best running back in the league when he sought a massive extension in 2011. There was a messy holdout before the Titans backed down. Their logic was that they had a rookie quarterback so there was cash to spare.

But this was one of the biggest mistakes ever. Johnson was their most important offensive cog and made the Pro Bowl for three straight seasons. He was also the 2009 Offensive Player of the Year. But after he signed a laughable $53 million extension he suffered immediate decline (via Bleacher Report).