The lead singer of Liverpool rock band The Zutons broke a man's nose after his girlfriend was insulted by a group of men, a court has heard.
Dave McCabe headbutted Peter Appleby in an alcohol-fuelled row outside a city nightclub, Liverpool Crown Court heard.
The 29-year-old admits hitting Mr Appleby but has claimed he acted in self-defence and denies assault occasioning actual bodily harm.
The Zutons formed in 2001 and have released three albums.
Ben Morris, opening the case for the prosecution, said the incident happened outside the Korova bar in Hope Street in the early hours of 21 February.
Jurors were told that one of Mr Appleby's five friends mocked Mr McCabe's girlfriend over her fur-collared jacket, claiming she looked like she had a beard.
She reacted "angrily" and Mr McCabe approached the group while Mr Appleby was laughing," he added.
"He never made the remark but he was laughing because he thought it was funny," said Mr Morris.
"McCabe came over and headbutted Mr Appleby, causing him a broken nose."
The court heard that Mr McCabe, of Vale Road, Liverpool, will tell jurors he was surrounded by Mr Appleby and his friends and believed he was about to be struck, so took the action in self-defence.
Giving evidence, Mr Appleby said the comment was not intended to be overheard and accused the woman of "over-reacting".
He described how Mr McCabe approached the group in an "aggressive" manner before shouting abuse.
"He seemed to be directing it at me and then he lunged towards me and headbutted me," said Mr Appleby.
Treated in hospital
He told the jury he had consumed six pints of Guinness and he was drunk, but denied doing anything to provoke the attack.
"I was stunned when he headbutted me. I looked down and all I could see was blood," he said.
Mr Appleby attended the Royal Liverpool Hospital for treatment.
Mr McCabe was arrested the following month.
During his police interview, he told officers he had wanted to make peace with the group and denied he attacked Mr Appleby in anger.
The case was adjourned and is due to continue on Tuesday, when Mr McCabe is expected to give evidence.