Bill Belichick took Eric Mangini under his wing in Cleveland. Back in the early 90s, Belichick was just starting out his head coaching career while Mangini was a simple ball boy for the Browns. Out of that meeting bloomed a beautiful friendship that lasted for many years... until it was suddenly over.
The first step was Mangini leaving the New England Patriots to become the New York Jets’ next head coach. He then allegedly started recruiting assistants for his new gig on the flight back from the Patriots’ 2005 divisional round playoff loss in Denver, prompting the team to change the locks on the Gillette Stadium doors so that Mangini could no longer enter.
That was only the beginning, though. Mangini later also reported Belichick and the Patriots to the NFL for violating a vaguely-worded memo on camera positions. And so, what was once a close friendship quickly turned sour. And the rest is beef history.