BARRIE, ONT. -- The Ontario provincial police are appealing for witnesses to a violent arrest in Barrie's downtown.

The OPP started investigating the incident that happened on Dunlop Street on Feb. 4 at Barrie Police Chief Kimberley Greenwood's request.

Video of the arrest taken by a bystander was widely circulated on social media and showed a Barrie police officer trying to detain a 20-year-old man.

The officer struggled on the ground with the man while holding what appeared to be a stun gun and hit the man's head with the device.

The video doesn't show what lead up to the arrest.

The officer involved was reassigned to alternate duties pending the outcome of the investigation.

The OPP is hoping to speak with anyone who saw the incident firsthand.

Anyone with information is asked to contact provincial police at 1-888-310-1122.