Todd Keith Rheinberger, 32, fronted the ACT Magistrates Court last Thursday after pleading guilty to one count of assault occasioning actual bodily harm.

Agreed facts tendered to the court stated Rheinberger was with a group of friends at the SummerSalt concert at Commonwealth Park on February 27 last year when the incident occurred.

About 8.50pm that day, the victim was cleaning up rubbish, including alcohol cans, near Rheinberger and his friends when there was a discussion about the rubbish.

The offender yelled "how about you f--- off, mate?" at the victim before striking him in the head while he stood up from bending down.

Rheinberger, whose criminal history includes two previous assault convictions, left the scene while the victim lost consciousness for a short period.

He was also diagnosed with a subluxation of the jaw, which is a dislocation that immediately relocates, after being taken to hospital.

The next day, Rheinberger messaged a mutual friend to send his apology and to ask if he could help the victim.

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In court, Magistrate Peter Morrison said it was an aggravating factor that the assault happened in public.

"It's an aggravating factor that that your blow was struck immediately as the victim stood from bending over and without warning," Mr Morrison said.

"He had no opportunity to defend himself. In that respect, your attack was a cowardly one. Your response was wholly disproportionate to any mild irritation there might have been."

The magistrate said he accepted the offender's remorse, albeit the following day and not immediately after the attack, and said the conduct was not premediated.

Mr Morrison sentenced Rheinberger, who was born in Canberra and is a national construction manager, to 120 hours of community service to be completed within 12 months and to pay the victim $1205 within 30 days.

He told offender to regard himself as "extremely fortunate that the injuries to the victim were simply not more serious".

"We see and hear every day [about] several punches resulting in death ... and of course if that were to happen, we'd not be here talking about community service," he said.

Earlier in the hearing, defence lawyer James Maher said his client was a devoted family man, a role model and "someone who goes out of his way to help people less fortunate".

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