WA man dodges jail for one-punch attack

A man who broke another man's jaw in a one-punch attack after a night out south of Perth has been spared an immediate jail term.

Jayden Brook Stephens was 19 when Jordan Lee Glasper, 24, attacked him as he tried to say goodnight to a mutual friend in Mandurah in August.

Glasper was drunk after celebrating his birthday and wrongly believed his friend was in danger after seeing Mr Stephens follow the man as he walked away.

The victim lost a tooth a now has a metal plate in his jaw.

"He became protective and was worried that something would happen and has said he's the one who has become the instigator at that point, which is unfortunate," his lawyer Stephen McGrath told the District Court of Western Australia on Friday.

"It was something where he's just taken at things the wrong way and misunderstood the situation at hand."

Justice Kathleen Glancy sentenced Glasper to 18 months' imprisonment, fully suspended, with conditions.