Carson Palmer
It’s amazing the difference that one player can make to an NFL season. The Cardinals discovered this the hard way in 2014 as they blazed their way to a 9-1 start. On paper, it appeared that they would be contenders at the business end of the postseason. But then out of nowhere Palmer tore his ACL.

Then they immediately fell into a malaise and won just two of their remaining games. His injury ruined their genuine playoff hopes as they struggled to make passes. It’s a shame because backup Ryan Lindley wasn’t in Palmer’s class. They snuck into the Wildcard Round but lost to the Panthers (via Sports Illustrated).