Matt Damon and Ben Affleck have been friends since their childhood, and Damon shared the fascinating — and quite violent — story of how they became pals during a sit-down with fellow Boston native Conan O’Brien.

Appearing on Conan, the 49-year-old “Bourne Identity” star revealed that he and a group of neighbourhood kids were playing football on Cambridge Common during a snow day in the 1980s when an altercation occurred.

“I mouthed off to this kid that I knew, but he was like your [Conan’s] height, like six-foot-six, and I might have been five-three at the time, and I said something,” Damon told O’Brien. “I’d scored on him or something, and I don’t know, I said something but he came for me. And it was like this mountain of a guy came at me and I was like, ‘Oh man.’ So before I knew it, it was like I was on the ground, he was above me, and I was like, ‘This is gonna be bad.’”

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Help arrived in the unexpected form of Affleck. “It was right then that little five-foot-two Ben Affleck tackled this dude off of me, like out of nowhere,” he recalled. “I was, like, a junior and he was, like, a freshman, and he tackled this kid off of me, literally at the risk of his own life.”

Added Damon: “But I remember that was a big moment, going like, ‘This guy, he will put himself in a really bad spot for me.’ Like, ‘This is a good friend to have.’”

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