ESPN is releasing a 30 for 30 on the relationship between Bill Belichick and Bill Parcells, which should be amazing.

If you’re not all that familiar with their relationship, here’s the main thing you need to know: Parcells was a total jerk to Belichick. The two did not get along at all but that didn’t stop them from building great defenses and winning a lot of games.

Belichick was Parcells’ defensive coordinator with the Giants, Patriots and Jets. The latter would routinely blast the former over the coaching headset with all of the other coaches on the staff listening. One tongue lashing was particularly brutal and may very well have been the reason Belichick decided to spurn Parcells and the Jets and flee for New England.

The relationship between the Bills had grown especially contentious during their time together with the Jets. Belichick had his guys on the staff — mostly guys he had worked with during his stint as the Browns head coach– and Parcell had his. The two sides clashed. Things boiled over during a game in their first season back in New York when Belichick drew up a blitz Parcells did not like.

From David Halberstam’s “The Education of a Coach”:

There was one terrible moment, during a game, when Belichick called a blitz, and Parcells seemed to oppose it. They went ahead with it and the blitz worked — the other team had done what Belichick expected and not what Parcells had — but Parcells was furious, and over the open microphones in the middle of a game, he let go, “Yeah, you’re a genius, everyone knows it, a goddamn genius, but that’s why you failed as a head coach — that’s why you’ll never be a head coach… some genius.” It was deeply shocking to everyone who heard it; they were the cruelest words imaginable.

Belichick ended up proving Parcells wrong, obviously. He resigned a day after Parcells gave him the head job in New York, taking the same position in New England, where he’d lead the Patriots to five Super Bowl wins (and counting.)

If you can’t wait for the ESPN doc, I recommend checking out Halberstam’s book on Belichick. It’s a must read for any football fan.