According to TMZ:
We’re told Campus Police took the music mogul into custody early Monday afternoon. Diddy’s son, Justin Combs, is a defensive back on the team. We’re told the fight went down at the UCLA athletic facility.
One source says an assistant coach was screaming at Justin on the field during a strength and conditioning session. We’re told the coach “was riding Justin, screaming intensely at him.” Diddy watched the whole thing from the sideline.
At some point later, we’re told Diddy confronted the coach in his office and grabbed him. Diddy was arrested for assault.