Sources familiar with the situation say that Bieber was at a party hosted by Patrick Schwarzenegger on Saturday night, when a man walked in, saw a woman, and "went ballistic", per reports.
Apparently the raging "ex" waltzed into the party, immediately spotting the woman in question. However, it appears someone tried to killed his vibe after he was forced to get involved in a fight to rescue a woman from an abusvie man.
TMZ also learned that his antics didn't simply die down after his party ejection.
The guy, who was said to be on drugs, was thrown out of the party and a short time later, was chasing an SUV, thinking Justin was inside. Police caught up with the crazed individual shortly thereafter, arresting him on the spot. He was screaming Justin's name as he began hitting the vehicle. We're told cops eventually came and arrested him. Metro.co.uk has contacted reps for Justin for comment.