Answer
Matt Cassel became a starter due to Tom Brady's injury in the 2008 season. In the second game of the season, Brady suffered a torn ACL and MCL, which required season-ending surgery. Cassel was named the starter for the remainder of the season. He went 10-5 as a starter, and led the Patriots to the AFC Championship Game. However, the Patriots lost to the Steelers in the AFC Championship Game.