Hiring position coaches almost never works out. Of the possible jobs a coach can have prior to making the leap to head coach — head coach with another team, coordinator, position coach, or college — position coaches fare the worst by a significant margin. There have been just 14 position coaches to make the jump to head coach in the salary cap era. On average they have produced a Pythagorean win percentage of .451, well below coordinators (.492), head coaches (.509), or college hires (.516).
There have been just two coaches who have made a successful transition from position coach to head coach in one season: Jim Caldwell with the Colts and Jeff Fisher with the Oilers.
Caldwell's success can be explained with two words: Peyton Manning.
You could make an argument that Fisher doesn't qualify at all. After spending time as the defensive coordinator for the Eagles and Rams between 1988 and 1991, Fisher took a step back to become the defensive backs coach in San Francisco under George Seifert in 1992, where he remained for two seasons. In 1994, Fisher took another coordinator position, this time in Houston under Jack Pardee. Pardee was fired after 10 games, and Fisher began his 17-year run as the franchise's head coach.
Outside of those two, it's a pretty terrible lot that includes the likes of Mike Singletary, Jim Zorn, and Rod Marinelli.
The other move that seems to generally be a bad idea are internal hires. Twenty-one of the coaches in our sample were internal hires and their .421 Pythagorean win percentage was the worst split I looked at by a wide margin. Sorry, Jim Tomsula. Being a head coach just might not be your thing.
http://www.ninersnation.com/2015/1/9/7519139/searching-for-the-profile-of-a-successful-nfl-head-coach
