A rock fan beat a fellow gig-goer unconscious after a row over the "glare from his bald head spoiling the view of the band", a court was told.
Andrew Ridley, 56, is accused of attacking the unnamed man at the O2 Academy in Birmingham in 2019.
The alleged victim was knocked unconscious and suffered a bleed to the brain as a result of the incident.
Ridley, 56, of Northfield, Birmingham, has denied causing grievous bodily harm with intent and an alternative charge of inflicting grievous bodily harm.
Philip Beardwell, prosecuting at Birmingham Crown Court, said that on 19 April 2019 a rock bank called Monster Truck had played at the O2 Academy in the city.
The alleged victim had gone to the concert, which was quite busy, along with his brother while the defendant was also there.
Mr Beardwell told the court: "It seems that they were standing watching and there was a disagreement about who could see what.
"It was over lights shining off heads, something rather trivial you may think."
He said the verbal disagreement then became physical with the alleged victim pushing the defendant.
Ridley responded by allegedly punching him and he fell to the ground and was knocked unconscious, the court heard.
"Ridley got on top of him and continued to punch him," the prosecutor said.
He said he was taken to hospital because of the attack, where he was kept for three days.
His most serious injury was a bleed to the brain revealed by a CT scan, while he also suffered swelling across the left side of his forehead, cuts behind both eyes, a chipped tooth and swelling to his jaw.
When later questioned, Ridley said: "He hit me first so I hit him back."
Giving evidence, the alleged victim said he had also gone to the rock concert with three friends.
He said: "It was standing. The only thing I can remember is having a conversation with a man behind, he either tapped me on the shoulder or nudged me.
"He said that he could not see the band because of the glare off my bald head.
"It was offensive to me, a perfect stranger to say something like that."
He said that the man had made the comment about two or three times and that the next thing he remembered was waking up in hospital, the court heard.
In cross-examination, he said he could not remember pushing the man, although someone had told him he had done that and that he had taken the comment as an "insult."
The alleged victim's brother said he had seen his sibling push the other man who had struggled to remain on his feet.
However, he said, the man had then punched his brother to the head with full force and that he had gone straight to the ground.
He said he had been "shocked" and that someone else had pulled the man off his brother, the court heard.
While Jeremy Wood, another concert goer, said he became aware of a disturbance behind him and said "I saw a man assaulting another man viciously."
The trial continues.