According to sources, Biebs was at a party Saturday night, and he saw a man who appeared to be on drugs walk in and went crazy on a lady.
Justin and a friend allegedly began screaming at the guy to let her go, but the man wouldn't let go of his grip. When that happened, it's said Justin hit the man and pushed him against the wall and the woman got free.
It's said after the incident the guy was thrown out of the party, and it's rumored that he began chasing an SUV he thought contained Bieber. Cops allegedly arrested him later that evening.