Kiefer Sutherland headbutts fashion designer to defend Brooke Shields

Kiefer Sutherland

headbutting case at the big Metropolitan Museum of Art Costume Institute's Gala Monday night.

Law enforcement sources told TMZ that Sutherland headbutted a man to defend

Brooke Shield

s's honor.

It all went down at an after-gala party, when witnesses said the alleged victim - Proenza Schouler designer

Jack McCollough

- knocked Shields over and Sutherland saw it happen.

Witnesses said Sutherland told McCollough to apologize and when the designer pushed the "24' star, Sutherland headbutted him. McCollough was seen nursing a broken nose when leaving the First Precinct in Lower Manhattan Tuesday night, according to NYC media reports.

Police are investigating the incident and Sutherland hadn't been interviewed as of Tuesday night.

In the meantime, Shields' representative told TMZ Tuesday night that McCollough did nothing to warrant the alleged attack. "Nothing happened to her," the actress' rep said, adding "Jack did nothing inappropriate. It's not clear what caused Kiefer to do what he did."

Police apparently plan to interview Shields on Wednesday.