The young man detailed these, along with many more consequences of the attack perpetrated by Jese Smith-Shields, in a victim impact statement read to the ACT Supreme Court on Thursday.

Smith-Shields, a 22-year-old who once aspired to be a professional rugby league player, was found guilty last month of assault occasioning actual bodily harm over the 2018 incident at Spilt Milk.

He was cleared, however, of the more serious charge of recklessly inflicting grievous bodily harm.

This could only be because a jury rejected his claims that he threw the knockout punch in self-defence, but found that he had lacked the criminal intent required for a guilty verdict on the primary charge.

The court heard during Smith-Shields' trial that the altercation had stemmed from "bad blood" linked to unsubstantiated rumours that his ex-girlfriend had slept with the victim.

The 22-year-old's friend Bayley Loughhead stood trial alongside him and was found not guilty of both charges.

Smith-Shields' sentencing proceedings began on Thursday, when Crown prosecutor Trent Hickey read statements from the victim and his mother.

The victim said the assault had left him unable to eat anything but pureed food for several weeks.

He also described suffering regular headaches as a consequence, as well as night terrors in which he imagines someone chasing and trying to hurt him.

The man said two years on, he still did not understand why he was assaulted.

"I thought we were mates," he said of Smith-Shields.

The man went on to detail how he felt "totally useless" while unable to work and provide for himself in the aftermath of the incident.

He had to give up his passion of playing rugby league because of his injury, and was unable to train at the gym for a time in what he said was a big blow to his mental health.

His jaw still regularly "clicks" and hurts, but he plans to live with the pain rather than undergo further surgery because he does not want to spend more time away from work and the gym.

Despite all this, he said he was grateful that he did not end up dead or with a brain injury.

"I keep thinking over and over again, what if I didn't wake up?" the man said.

Mr Hickey urged Justice John Burns to sentence Smith-Shields to a jail term, even if it was suspended, arguing that a good behaviour order on its own would not be a strong enough penalty.

He said it was important to deter others from similar offending after such a public incident that involved "a targeted and direct blow to the head".

Mr Hickey also asked the judge to rely on the account of a particular witness, who described the knockout blow as having been delivered "in a king hit fashion".

He then highlighted the fact that "the offender decamped from the scene quickly" after landing the knockout punch, saying it was evidence of "the negative state of mind he had on the day".

But Smith-Shields' barrister, Beth Morrisroe, argued that her client had clearly demonstrated remorse by quickly contacting the victim and his mother in a bid to check on his welfare.

She said that even though the jury had rejected Smith-Shields' self-defence argument, Justice Burns could be satisfied that the victim had shown "a level of aggression" and that the assault had not been premeditated.

There were also too many conflicting accounts, including one of "a fight with two-way input", Ms Morrisroe said, for the judge to be sure there had been a "king hit".

In arguing against a jail sentence, she tendered to the court 14 character references praising Smith-Shields as a normally responsible young man with leadership qualities.

Smith-Shields is expected to learn his sentence next Friday.