Pete Carroll (Seattle Seahawks)
That’s right. We’re going there. The greatest coach in Seattle Seahawks history is also a major underachiever. Think about this. By 2013 when he won his first championship, the core the Seahawks had in place was ridiculous. The defense alone was loaded with All-Pros and possible future Hall of Famers like Earl Thomas, Richard Sherman, Bobby Wagner, Kam Chancellor and Michael Bennett.
Then you throw a potential Hall of Fame quarterback in Russell Wilson on the other side of the ball with an All-Pro running back in Marshawn Lynch and future Pro Bowl receiver in Doug Baldwin. This had the look of a dynasty in the making, and it almost was. Until Carroll ruined it. His decision to throw the ball at the goal line in Super Bowl XLIX, the play that resulted in the iconic Malcolm Butler interception, fractured the team beyond repair.
A lot of players held and continue to hold that against him. Soon the core began to fall apart and the Seahawks are a shell of what they once were.