The victim was on a night out at Mooseheads on London Circuit in June last year. Orry Kuzma, 19, was also in the club and had been drinking. Kuzma walked up to the victim and, in an ''entirely unprovoked'' attack, delivered a single punch to his face.

The blow, described in court as a ''king hit'', was unexpected and the victim did not know Kuzma in any way. It knocked the victim unconscious and he was left bleeding heavily from his head.

The young man had fractures to his nose, eyes and face and he suffered swelling to his eye.

Doctors were forced to surgically install metal plates in his face.

Kuzma is now being sentenced in the ACT Magistrates Cour for a negligent act causing grievous bodily harm.

In a sentencing hearing on Monday, the prosecution described the attack as ''unprovoked'', ''vicious'' and a ''gratuitous act of violence''.

The victim's father broke down as he read out a statement written by his son's mother.

She wrote of how the attack had haunted her ''for a very long time''.

The mother wrote of the anxiety and fear she felt when she received the phone call telling her that her son had been punched.

''That night was when my worst fears were realised,'' she wrote.

''The sense of panic was overwhelming.''

But she said that was nothing compared with the image of the ''battered, bruised and crushed'' face that confronted her when she got to hospital. ''What had he done to deserve this?'' she wrote.

''It is an image I'll never forget.''

She spoke of how she now constantly thought of the ''what ifs'' and dwelled on whether he would be dead if his head had smashed into the ground. ''Barely a day goes by when it's not on my mind.''

Kuzma's lawyer, Kamy Saeedi, submitted to the court that it should take into account his client's youth, good prospects for rehabilitation and diagnosis of a major depressive disorder.

Mr Saeedi said Kuzma was undergoing counselling and had written a letter of apology to his victim, which could not be delivered because of bail conditions.

The teenager had also made full admissions to police and pleaded guilty at the earliest opportunity to the charge he was now facing.

Mr Saeedi said the court should not impose an immediate term of imprisonment.

He said the offence was only a single punch, rather than a sustained attack.

The prosecution argued that little weight could be given to Kuzma's diagnosis of depression, given there was no causal link with the violence.

It said the teenager had pleaded guilty only after negotiations and once he realised he faced an ''overwhelmingly strong prosecution case''.

The prosecutor said Kuzma seemed to show little to no remorse and the teenager told a pre-sentence report author that he had not really thought about the impact of his attack on the victim.

Magistrate Robert Cook was urged by the prosecution to reflect the community's denunciation and sense of outrage in his sentence.

The prosecution said people had the right to go out and feel safe and to go home safely and not be set on by a stranger.

Mr Cook is expected to hand down his sentence on Wednesday.