Rhyce Bailey Butcher Corney, then aged 18, was in Dunsborough for school leavers celebrations on November 20 last year when his friends and another group became embroiled in a dispute.

Butcher Corney claimed he was startled by teenager Andrew McNab, who suddenly appeared to the side of him, and took a swing, the West Australian District Court heard.

He pleaded guilty to causing grievous bodily harm and was sentenced on Tuesday to 15 months in prison, suspended for 20 months with strict conditions.

Defence counsel Linda Black previously said her client, who has played football for the Swan Districts colts, pleaded guilty and had been "to hell and back" since the incident.

The court heard Butcher Corney was on bail for this offence earlier this year when police saw him throw a bottle in the direction of his girlfriend following an argument.

It resulted in him spending 78 days in prison until the charge was downgraded and he was fined $500.

Ms Black said Butcher Corney was terrified in prison.

"He looked like he was about to pass out," she said.

"Mr Butcher Corney has had a wake-up call of his life."

Referring to the victim impact statement, Judge Stephen Lemonis said Mr McNab had suffered trauma and still had numbness in his face.

Judge Lemonis accepted Butcher Corney was genuinely remorseful and had taken steps for rehabilitation.

But general deterrence was also a significant factor, he added.

"You came very close today to going back to prison," Judge Lemonis said.

The judge warned Butcher Corney that if he breached his conditionally suspended sentence it would be "almost inevitable" that he would return to prison.

Outside court, Mr McNab said he was disappointed with the sentence and was yet to receive an apology.

"I'd like to see him go to jail, of course," he told reporters.

"I'm stuck with metal in my face. I mean, I still can't even feel my face."

Australian Associated Press