this from the official rolling stones site:

Dec 6: The Stones arrive at the Altamont Speedway track just outside San Francisco for a free concert. After a few numbers, a spectator takes a gun and aims it at the stage. He is immediately pounced on by Hell's Angels security. The band restarts the concert, but more trouble breaks out as the Angels run rampant through the audience. Keith stops playing and announces, "Either those cats cool it, man, or we don't play." The Hell's Ang els around the stage start to circle the band. With his usual diplomatic flair, Keith notices the burliest of the encroaching Angels and says only, "Fuck you." Surprisingly, the posse backs off and the gig continues for another hour.

ahhh…the power of keith richards…