So here's the deal: apparently the two were hanging out at a bar in Seattle, when Paul McCartney started telling a story about the time he hit a guy. He was really getting into it, and ended up accidentally hitting Eddie Vedder in the face while demonstrating how it all went down.
“A great time in my life, to be hit by Paul McCartney,” Vedder said. “I remember it hurt for a few days, And I remember when it went away, when the pain finally subsided and the swelling went down, I kinda missed it.” (EW)