A police officer who accidentally struck a teenage motorcyclist with his car during a traffic stop in Adelaide's north has had a dangerous driving conviction overturned.

Key points: Benjamin Wormwell spent 10 weeks in hospital after he was hit by a police car at Parafield Gardens

Benjamin Wormwell spent 10 weeks in hospital after he was hit by a police car at Parafield Gardens The driver, Senior Constable Matthew Lumsden, accidentally hit the accelerator instead of the brake during a traffic stop

The driver, Senior Constable Matthew Lumsden, accidentally hit the accelerator instead of the brake during a traffic stop He was found guilty of aggravated driving without due care but that conviction has been overturned

Senior Constable Matthew Lumsden was responding to a report of drag racing when he came across two riders on Macartney Road at Parafield Gardens in May 2017.

During a trial earlier this year, the Elizabeth Magistrates Court was told Senior Constable Lumsden failed to put his police car into park and when it rolled forward, he mistakenly hit the accelerator instead of the brake.

The car then struck Benjamin Wormwell, who was 17 at the time, before mounting a kerb and rolling onto a footpath.

The car came to a stop between a tree and a fence.

Mr Wormwell spent 10 weeks in hospital with multiple broken bones and had screws inserted in his pelvis, as well as a rod in his femur.

Magistrate Sue O'Connor found Senior Constable Lumsden, of the Road Policing Section, guilty of aggravated driving without due care.

In handing down her sentence, she acknowledged a six-month loss of licence would have a "marked impact" on his policing career.

SA Police officer Matthew Lumsden successfully appealed against his conviction. ( ABC News )

But Supreme Court Justice Tim Stanley overturned the conviction, finding he was protected by the Police Act, which grants officers immunity "from criminal liability for the honest performance of their duties".

"An immunity from civil or criminal liability is not conferred upon a member of SA Police for every honest act or omission, but only those in the exercise or discharge [of their duties]," Justice Stanley said.

Justice Stanley said he was satisfied that Senior Constable Lumsden was performing a traffic stop at the time of the incident.

"In this case the [officer] believed the circumstances to be that he had placed the transmission into park," he said.

"Accordingly, the magistrate should have returned a verdict of not guilty.

"It follows that the conviction must be set aside and a verdict of not guilty substituted."