A Perth police officer is on trial accused of using excessive force whilst arresting a man more than four years ago.

Constable Adam Wiringi is alleged to have broken the jaw of 24-year-old David Barnard in the Perth suburb of Kiara in February 2007.

The District Court has been told Mr Barnard was knocked off his BMX bike onto a driveway before allegedly being pile driven head first by Constable Wiringi into the ground.

The court heard police had been chasing him because he was riding his BMX bike without wearing a helmet.

Mr Barnard has testified that just before the alleged assault, he heard Constable Wiringi yell, "wait until I get my hands on you".

He also told the court he was then taken to Kiara police station where he was refused medical assistance.

After being released Mr Barnard went to hospital and eventually had an operation to insert a metal plate in his jaw.

Constable Wiringi has denied any wrongdoing.

The trial continues tomorrow.