A man has been given a suspended sentence for a "coward punch" assault at a Canberra pub that the magistrate described as "unforgivable".

Logan Dunlop, 21, was given an eight-month suspended jail term in the ACT Magistrates Court on Friday for assault occasioning actual bodily harm.

He was given a 12-month good behaviour order and 200 hours of community service.

Security footage shows Dunlop walking through the crowd at a pub with his girlfriend in April 2013 before stopping, spinning around and then quickly starting his assault.

The footage shows Dunlop punching an unsuspecting university student in the face before continuing to hit him around the head as he lies on the ground.

The incident only lasted a few seconds but it left the victim with a broken eye socket and severe bruising and cuts.

Logan Dunlop and lawyer Peter Woodhouse leave the ACT Magistrates Court. ( ABC News )

Prosecutors say the victim could have permanent damage to his eye.

Dunlop pleaded guilty to the charge and explained that he had no justification other than he thought the man had insulted his girlfriend.

"I just feel really bad," he said.

"At the time I was very angry... I've learnt from my mistake."

Dunlop's lawyer Peter Woodhouse explained that the charge meant his client could no longer follow his two parents into the police force.

"Would it be fair to describe you as a violent drunk?" Mr Woodhouse asked.

"No," Dunlop said.

But Prosecutor Anthony Williamson described the attack as "vicious and intense".

"Another unfortunate example of senseless, gratuitous... alcohol-fuelled violence," he said.

"It started with a king hit, or as the media likes to call it now a 'coward punch'.

"[The victim] had no opportunity to see it or protect himself."

In Magistrate Beth Campbell's sentencing remarks, she spoke of the recent media coverage of alcohol-related violence.

She said it clearly pointed to a frustration in the the community over trying to end such assaults, but noted that she must not impose a more significant sentence because of the coverage.

But Ms Campbell did make mention of the 'irony' that Dunlop has two police officers as parents.

"I accept that he doesn't fit the stereotype of young men being paraded before the courts in other jurisdictions," the magistrate said.