Prime Taskforce detectives are investigating the assault of a PSO during a protest in Richmond earlier this year.
The PSO was working alongside police officers to manage public order on Bridge Road on 18 September.
A male protester has emerged from the crowd and run straight for the PSO, ramming him with his shoulder.
He then punched the male PSO to the face before running back into the crowd.
The PSO sustained minor injuries during the attack.
Investigators have released images of a man they believe may be able to assist with their enquiries.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au