He may not look like much of a fighter, but Pete Wentz is a card carrying member of the Russell Crowe Club of Celebrity Brawlers. A fight broke out at Sunday's Fall Out Boy show in Albuquerque, NM, and the bassist jumped into the crowd and punched a security guard in the face, Perez Hilton reports.

Get the blow-by-blow from a concertgoer, who wrote about the experience (and posted a video of the fight!) on his MySpace.

"At the end of their set during 'Saturday,' they started letting people onstage. Security didn't want anymore ppl on stage. A roadie (and comrade) of FOB's was still letting ppl on. That must have pissed off a certain securty guard enough to attack the roadie and bring him offstage and grapple with him. Pete took offense and dropped the mic, jumped offstage and started beating [him]...After the pummel, Pete got back onsatge, grabbed the mic and stated, 'That's what you get when you [mess] with my friends...' then the band left…"

Geeeez. We guess you can't say that Pete Wentz doesn't care about his fans!