This is the video of Frank Mir breaking Tim Sylvia’s arm at UFC 48.
Back in June 2004, Sylvia faced Frank Mir for the vacant UFC heavyweight championship. Mir trapped Sylvia’s right arm in an armbar attempt. When Sylvia tried to pull out of the hold, Mir jerked back harder and Sylvia’s radius bone snapped about 3 inches below his elbow. Herb Dean quickly stopped the fight. Sylvia repeatedly claimed his arm was not broken, even touching it and moving it around to show he was O.K. Sylvia was taken to the near by hospital where an x-ray showed that his arm was in fact broken.