kiefer_sutherland_011.jpgKiefer Sutherland reportedly headbutted a man at an after-party following the Costume Institute Gala in New York on Monday night.

The 24 star is said to have attacked designer Jack McCollough, co-founder of Proenza Schouler, at the event at SubMercer in the early hours of Tuesday morning.

Initial reports claimed Kiefer felt provoked after McCollough bumped into Brooke Shields so hard that she was knocked to the ground - but spokespeople for both Brooke and McCollough say “nothing happened to her”.

One eyewitness is quoted in the New York Post as saying: “Sutherland was really drunk and he got accidentally bumped by McCollough. They started arguing and then he just head-butted him.”

Another source added that earlier in the evening, Kiefer had been acting strangely in the Gramercy Park Hotel’s Rose Bar: “He was running around wearing a giant feather boa and acting totally crazy. He was dancing feverishly and twirling people around all over the place. He seemed to be quite intoxicated.”

A source close to Kiefer told the New York Daily News: “when Kiefer gets drunk he gets belligerent. If he was drunk, none of this surprises me.

“He sticks to water in public but in private he goes right to the booze and gets angry and violent. When he’s drunk, people are afraid to be around him.”

McCollough is said to have suffered a broken nose in the incident, with police investigating what happened. Other guests at the party included Kirsten Dunst and Mary-Kate Olsen.

Kiefer is currently on probation for his 2007 DUI charge.