Ranking Detroit Lions head coaches since 2000
6. Bobby Ross (2000, 5-4 record before resigning; 27-30 overall as Lions head coach)
The 2000 season was the last of four for Ross as the Lions' head coach, and he resigned before it was over when the team was 5-4. Gary Moeller, the former University of Michigan head coach, finished out a season that actually wound up being a winning one (9-7, but with no playoffs).
The game had surely passed Ross by at the end of his Lions' tenure, and he resigned before he probably would have been fired after the season. But after his departure, a very ugly course for the franchise for quite a while came, as the Lions posted double-digit losses in all but one season from 2001-2010 (7-9 in the lone expection).
5. Rod Marinelli (2006-2008, 10-38 record)
Marinelli made his hay in coaching on the defensive side of the ball, highlighted by a run with the Tampa Bay Buccaneers as defensive line coach before landing his head coaching job in Detroit at the age of 56.
Marinelli was simply not cut out to be a head coach, and it consistenly showed over three seasons. The Lions going winless in 2008, the first 0-16 season in NFL history, sealed his fate. But even if the team had won a few games, he was not getting a fourth season as head coach.