Christopher Hollosy's trial began Thursday in Superior Court.
Both men were arrested in October after a man accused them of punching him outside a Washington hotel. Hollosy told police he punched the man after he tried to get on Brown's tour bus. The man told police Brown and later Hollosy punched him after he tried to get in a photo Brown was taking with two women.
Court papers say the man's nose was fractured.
Hollosy's trial is expected to last one to two days. Brown's trial will follow. Brown has denied punching the man.