Jese Smith-Shields, 22, wiped away tears in the ACT Supreme Court on Wednesday afternoon as the jury foreman declared him guilty of assault occasioning actual bodily harm.

He had been found not guilty moments earlier of recklessly inflicting grievous bodily harm, while fellow 22-year-old Bayley Loughhead was cleared of both charges.

The duo had been on trial for more than a week after a man they knew suffered a broken jaw at Spilt Milk in 2018.

The prosecution case was that Smith-Shields and the victim were at loggerheads over rumours about a woman when they saw each other at the music festival.

It was alleged that Smith-Shields punched the victim, knocking him out and breaking his jaw, and that Mr Loughhead had assisted the assault by holding the victim in a headlock.

Smith-Shields' barrister, Beth Morrisroe, argued that "115 kilograms of muscle" had aggressively "charged" at her client, intent on hurting him, leaving Smith-Shields with no option but to throw a punch in self-defence.

Jack Pappas, representing Mr Loughhead, contended that his client had merely become involved in the confrontation to defuse things. He said it was not clear whether Mr Loughhead had ever put the injured man in a headlock, but said that if he had it would have been in an effort to quell tensions.

After the jury returned its verdicts, Justice John Burns said the 12 citizens must have rejected Ms Morrisroe's self-defence argument in relation to Smith-Shields.

He said the jury must have concluded, however, that Smith-Shields did not act with the intent necessary for him to be convicted of recklessly causing grievous bodily harm, hence the verdict of guilty on the less serious charge.

Ms Morrisroe said she did not disagree with the judge's assessment.

Justice Burns continued Smith-Shields' bail, and set the matter down for sentencing on November 12.

The court heard that Mr Loughhead still faced a transfer charge of common assault, but that was likely to be withdrawn in the coming days and he would accordingly be discharged.