Norv Turner
When Norv Turner assumed control of the San Diego Chargers in 2007, they were the team to beat. The had a future star quarterback by the name of Philip Rivers who was just beginning to come into his own, and a Hall of Fame running back named LaDainian Tomlinson in the backfield. Somehow, he still managed to screw it up. He won 11 games in his first season and lost in the AFC championship game.
His only other season with 10-plus wins in 2009 when the Chargers went 13-3 and were defeated in the first round of the playoffs. Tomlinson, whose prime had already been squandered, left in free agency and the Chargers proceeded to miss the playoffs for the following three seasons before Turner was finally let go.