Here is my interpretation of yesterday's head-butting incident in the Tour de France. Mark Renshaw had his sprinter, Mark Cavendish, on his wheel. Julian Dean came alongside Renshaw on the right and began pushing him (with his bike, elbow, and shoulder) toward the barrier. The obvious intention was to trap Cavendish behind his own lead-out man, thus giving Dean's sprinter, Tyler Farrar, a clear line to the finish. To hold his line, Renshaw had to use his head against Dean. This worked. Dean moved right, back into his line, and Cavendish moved through the gap on the left. Renshaw's head butting was purely defensive. Dean should have been either relegated to last place or disqualified from the Tour.
But then Renshaw did a bad thing. Once Cavendish had been sprung, Renshaw moved left, out of his line. Whether this was intentional I don't know (Renshaw denies it), but the effect was to pinch Farrar against the barrier, which ensured that he would not contest the sprint. Renshaw should have been either relegated to last place or disqualified from the Tour. Watch this video and comment on my interpretation. Please do not confuse the two actions by Renshaw. First there was the head butting, which was innocent (a matter of self-preservation), and then there was the pinching of Farrar, which was not innocent.
I should add that when I first saw the head-butting incident, I blamed Renshaw. Having studied the video carefully, I believe that Dean was in the wrong and Renshaw innocent.
Addendum: As for why nearly everyone is blaming Renshaw, it's for the same reason that they would blame A for hitting B if they hadn't seen B hit A a moment before. Head butting can be either offensive or defensive. I believe Renshaw's head butting was defensive, and therefore perfectly acceptable. What is he supposed to do, allow another rider to push him over? He had every right to continue in a straight line.
Addendum 2: Here is Renshaw, immediately after the finish. Notice that he accuses Dean of "coming across" on him. Exactly. At that point, he had the following choices: (1) reach out with his hand and push him away; (2) head butt him; (3) allow himself to be pushed against the barrier.
Keith Burgess-Jackson, J.D., Ph.D. 