The Weeknd ARRESTED ... For Allegedly Punching a Cop

R&B singer The Weeknd was arrested Saturday in Las Vegas ... after he was accused of punching a cop. Law enforcement sources tell us a fight allegedly involving Weeknd started inside the Cromwell Hotel around 4:20 AM ... and when they arrived, the fight was still raging. We're told cops attempted to break up the fight, and one of them pulled the singer into an elevator during the scuffle.