It's one of the many hidden gems in NFL Films' documentary, "Bill Belichick: A Football Life."
During a 2009 Patriots-Ravens game, Baltimore wide receiver Derrick Mason catches a pass near New England's sideline and runs out of bounds near Belichick.
Mason says a few words ... then a mic'd-up Belichick lashes out.
"F--- you Mason," he says. "Why don't we talk after the game, all right? Just shut the f--- up."
So, what prompted Belichick's outburst? In a 1-on-1 interview with our Tom E. Curran on Thursday at Tennessee Titans practice, Mason shared his side of that spat -- and insisted Belichick shouldn't have gotten involved in the first place.
"Here's the thing: None of it was directed at Bill," Mason told Curran. "It all had to do with Dean Pees."
Pees, the Patriots' defensive coordinator at the time, had a history with Mason, as he was on Michigan State's coaching staff (under head coach Nick Saban) while Mason was a Spartan.
And Mason says he was actually trash-talking Pees, not Belichick.
New England Patriots
Find the latest New England Patriots news, highlights, analysis and more with NBC Sports Boston.
"Dean Pees and I had a relationship. So, Dean Pees and I are going back at each other and I was laughing, because I enjoy having fun on the field," Mason told Curran. "I was laughing, and we were moving the chains. And I guess Bill just took exception to it, and Bill said something, and I laughed it off.
"Dean Pees and I talked about it (afterward), and I was like, 'It was you and I, coach, not him.' "
In Belichick's defense, Mason was running right past the Patriots coach while (supposedly) jawing at Pees, so we can understand the mixup here. And Belichick wasn't exactly in a cheery mood during the 2009 campaign, which ended in a 10-6 record and a Wild Card-round loss to Mason's Ravens.
But Mason would like to clarify that he didn't totally deserve Belichick's earful.
Click here to download the new MyTeams App by NBC Sports! Receive comprehensive coverage of your teams and stream the Celtics easily on your device.