A teenager had gone missing from State care when he took part in a "shocking" unprovoked street attack on a couple walking home from a night out.
Sean Costello, aged 16 at the time, was among four youths who set upon a man and woman in Dublin city centre.
He punched and kicked the man about the head after "jumping" on him while two girls attacked his girlfriend, Dublin District Court heard.
Judge John Hughes adjourned sentencing to find out what steps were taken to report Costello missing from the Dublin boys' home he was meant to be under curfew at on the night.
Costello (19), previously of Old Connell in Newbridge, Co Kildare, pleaded guilty to assault causing harm to the man and violent disorder.
The attack happened St Stephen's Green West at 4am on May 9, 2016.
Garda Niall Cunningham said the victims were set upon by youths aged between around 15 and 18. The two boys attacked the man while the girls allegedly attacked his girlfriend.
Costello was seen on CCTV kicking and punching the man several times in the head. The man suffered a black eye, bruising to his face and neck, and headaches.
The co-accused girls have been before the courts, while the other male was not found.
In a statement, the man said that he and his girlfriend had been returning from a club.
One of the girls asked the woman for a cigarette and one of "the lads" came running at the man and punched him in the face.
"I said, 'what did you do that for?' and the rest jumped on me," he said.
"I was absolutely in fear for myself and my girlfriend's safety.
"We did nothing to provoke the attack, we could see they were just looking for a fight."
Judge Hughes said the CCTV footage was "shocking".
Costello was abusing alcohol and tablets at the time and with a negative peer group involved in antisocial behaviour.
He was not the ringleader but was a participant.
"He was the last to leave, he went back for afters," the judge said.