Quoting other answers because I’m too lazy to type

He joined as the new head coach just before the Michael Vick dogfighting story broke and Vick left the team. So Petrino didn’t get the team and star player he thought he was getting. That year was going very poorly and instead of embracing the challenge Petrino bailed around 2/3 through the season and became head coach of a college team (Arkansas). He didn’t say goodbye to the players or anyone, just left in the middle of the night. Abandoned the team.

And then he got fired from Arkansas after getting caught sleeping with a team staffer after he crashed his motorcycle with her on it (and lied about it) One of the biggest pieces of human trash in football history, and that is saying a lot.