On Valentine's Day, my 18-year-old son Beau was coward-punched outside a Hindley Street nightclub in Adelaide. He was struck three times to the head. His attacker ran.

Beau now lives with a permanent traumatic brain injury.

On 29 September, the 17-year-old who attacked him was sentenced in the Adelaide Youth Court after pleading guilty to two counts of assault causing harm. The magistrate called it "pointless and avoidable", with "profound lifelong consequences".

He received six months' detention, suspended on a good behaviour bond. He walked out of court without serving any detention.

My son sits with a jail sentence in his head for the rest of his life, and that guy's now free to walk.

This outcome completely fails to reflect the severity of the offence, nor does it provide an adequate deterrent to youth violence.

I'm asking the South Australian Director of Public Prosecutions to appeal this sentence before time runs out.