CCTV footage of the alleged attack slap by Dappy on a man outside Chicago's nightclub in Chelmsford, Essex, was played to the court.
The black-and-white footage, which lasts about 10 seconds, showed the former N-Dubz singer "surrounded by security" when he turned and "slapped" George Chittock, Prosecutor Jaqueline Carey said.
Dappy, who's real name is Dino Costas Contostavlos, was acting out of "annoyance" in a "violent and unjustifiable manner" after claiming he was verbally abused during the night, she told the court.
Jon Harrison, defending, said early in the evening Mr Chittock told Contostavlos: "Dappy, you're a mug, I'm going to knock you out."
Mr Chittock replied: "Incorrect."
More top news
Coronation Street's Jimi Mistry revealed it was always the plan for Kal to be killed off after he made a fiery exit from the soap tonight.
Life for the Rohingya is one of suffering, writes Lucy Watson, as she explores why they are being driven into the arms of traffickers.
A motorist who boasted about clocking 142mph on a motorway shot through a red light and killed another driver the following night.