Justice Robert Pearce found Adrian Michael Johnson, 35, was not acting in self-defence when he punched Shane Baker while holding a glass, causing a deep laceration to the left side of the victim's face.

The Low Head man was sentenced to 15 months' jail, with six months wholly suspended for two years from September 24.

A five-month suspended sentence imposed in May 2017 was also activated, bringing the total jail time to be served to 14 months. He will be eligible for parole after serving half.

On May 27, 2019, both men were drinking at Grays Hotel with separate friendship groups and walked to a takeaway shop on Macquarie Street when the pub closed about 10.30pm.

When Mr Baker and his friend Luke Edwards left the shop they heard a commotion coming from the car park, so they walked over to check everything was OK.

A verbal exchange occurred when a woman with Johnson's group approached Mr Edwards aggressively.

As Mr Baker was suggesting to another woman in the group she calmed her friend down, Johnson hit the victim while holding a beer glass.

The two parties told conflicting stories about what happened in the car park, but Justice Pearce said during sentencing he found Mr Baker and Mr Edwards account was truthful.

"I found Mr Edwards, in particular, a compelling and persuasive witness. He was understated and not prone to exaggeration," Justice Pearce said.

Alcohol-fuelled violence was not out of character for Johnson, whose priors included assaulting a security guard at Devonport and assaulting his partner.

"The common theme amongst the offences committed by the defendant is his abuse of alcohol and proneness to violence when angered," Justice Pearce said.

It was noted Johnson claimed to be more aware of the management of alcohol and anger, but he hadn't sought any professional help.