Justin Bieber....ASSAULTED ANOTHER PERSON!!

Justin Bieber allegedly headbutted a guy at a pre-Grammy party last weekend, and cops are now investigating the incident as a possible crime.

Law enforcement sources tell us the alleged incident went down at 2 AM Saturday at L.A.'s Italian eatery, Serafina ... where Justin's producer pal, Poo Bear, was hosting a shindig.

Several eyewitnesses tell us Bieber was "play fighting" with Kyle Massey when he realized someone from the restaurant staff was recording the action. We're told Justin asked the guy to stop recording and delete the video. The staffer apparently resisted and some partygoers started recording as well ... that's when the eyewitnesses say Justin lunged at the guy. 

MORE INFO: TMZ
Filed Under :
Location : L.a.