Kiefer Experiences Headbutter's Regret

5/22/2009 3:20 AM PDT BY TMZ STAFF
He was allegedly defending Brooke Shields' honor with that well placed headbutt to designer Jack McCollough's schnoz -- but last night on "Late Night with Jimmy Fallon," Kiefer Sutherland admitted it's something he "really regrets having happened."

Kiefer & Jimmy: Click to watch