Jordan Charles Garcie, 20, was sentenced in February by magistrate Simon Brown to four months' jail, with eight weeks suspended.

Yesterday Garcie, who pleaded guilty to assaulting a 62-year-old man, appeared in Launceston's Supreme Court.

Justice Robert Pearce said he found the sentence to be manifestly excessive because it was not wholly suspended.

"A suspended sentence was what was necessary to meet the need for a sentence of denunciation and deterrence," he said.

Justice Pearce said an actual jail term was not warranted because of the nature of the attack, Garcie's own belief - however mistaken - that the victim posed a threat, the absence of serious injury and the offender's conduct after the assault.

He said Mr Brown was right to sentence Garcie on the basis that the force used was unreasonable.

The assault occurred outside a licensed venue in Launceston on July 6.

During the course of an argument, the victim took a step towards Garcie, who retaliated with a roundhouse elbow, the court heard.

The victim was knocked out immediately.

Justice Pearce said the four-month prison sentence handed down by Mr Brown was appropriate in the circumstances but actual custody was not.

The case comes as the state government prepares to abolish suspended sentences altogether.

Justice Pearce will resentence Garcie today.