Queanbeyan Local Court was told that Inspector John William Sheehan of the Southern Region was suffering from acute post-traumatic stress disorder and depression when he assaulted a juvenile suspect after a pursuit in Marulan, near Goulburn, in February 2012.

Magistrate Chris Bone was told that Inspector Sheehan was on patrol in a marked police car when the driver of an allegedly stolen vehicle drove towards his car at speed after a pursuit.

A 16-year-old driver was arrested by another officer after allegedly crashing the car in the area.

While the suspect was being held to the ground before being arrested, Inspector Sheehan kicked him twice in the head and yelled an obscenity.

The court heard the teen suffered no serious injury in the incident and there were no physical signs of the assault at the time of his interview.

Investigations by police and advice from the Director of Public Prosecution resulted in Inspector Sheehan being charged with assaulting a minor.

Magistrate Bone accepted medical advice that Inspector Sheehan, 43, was suffering from mental illness and "extreme pressure and strain" due to a number of incidents in his professional and family life in the months before the assault.

Lawyers for Inspector Sheehan described him as "an old-school officer" who only had his mental illness diagnosed after the incident took place.

"It wasn't gratuitous violence," Magistrate Bone said. "Actions taken by this man on the day was a form of revenge."

Ordering Inspector Sheehan to attend treatment for his conditions, Magistrate Bone said members of the public could have confidence in internal police procedures after the charges were laid without video footage of the incident or lasting injuries to the victim.

He said Inspector Sheehan had "breached a special trust" given to police officers by the community but that he was a person of good character who had been a serving New South Wales police officer since 1988.