The man's jaw was shattered and needed surgery after Jordan Sharma levelled him with a swift punch outside the East Row Supa 24 convenience store shortly before 3am.

Sharma, 20, handed himself in after ACT Policing released CCTV footage of the attack a week after it took place.

He originally pleaded not guilty to recklessly inflicting grievous bodily harm in the ACT Supreme Court but later switched his plea to guilty.

Court documents tendered at Sharma's committal said the footage showed the male victim, aged in his 20s, had an argument with a man as the offender stood nearby.

Sharma then clenched his fists, adopted a "fighting stance" and threw a single punch at the victim's jaw, causing the man to fall to the ground, the footage showed.

Police were called and found the man unconscious on the ground soon after.

Doctors had to insert a titanium plate and four screws into his jaw to fix the damage and it was wired shut for two weeks.

Sharma went to City police station in Civic several hours after the footage became public, admitting he was the person in the CCTV footage and that he threw the punch.

He returned to court for a sentencing hearing on Thursday.

Prosecutor Michael Reardon said the "unprovoked attack", on a man going about his business in a public place, could have resulted in far more serious injuries.

He said the fact Sharma could be seen "lining up" his victim in the seconds before he threw the punch showed there was an added degree of malice to what was often described as a "coward's punch" attack.

"It's not a case of the offender just lashing out," Mr Reardon said.

He said the man's injuries, which were inflicted with significant speed on a vulnerable part of his body, had a profound and lasting impact and had affected his quality of life.

"Seven-and-a-half months later there has still been no return to normality for the victim," he said.

Sharma's defence lawyer, Richard Davies, said the victim was recovering and there was no suggestion his injuries would cause long-term pain or disability.

He argued the attack was not premeditated, saying his client could not give any indication why he committed the attack and he had been intoxicated at the time.

Mr Davies urged the court to take into account Sharma's age, his lack of a criminal history, and the fact he had accepted responsibility for his actions.

He suggested a suspended sentence or intensive corrections order, which allow offenders to serve sentences in the community, would be appropriate.

Mr Reardon said the assault approached mid-range seriousness for offences of its type but accepted Sharma was young and otherwise of good character.

The court heard the attack had generated significant attention on social media after Sharma was reportedly named as the attacker in a post widely shared by online activist group Anonymous.

But the Crown argued there was no evidence that threats made as a result of that attention had stopped Sharma obtaining work or socialising.

Justice Michael Elkaim reserved his decision, He will hand down his sentence on Friday.