The incident happened near a bus stop on Glasgow Road near to its junction with Castlegreen Street, Dumbarton on Wednesday, June 2 at around 6.45pm.
A 40-year-old was initially involved in an altercation with a man – believed to be 17-18 years old – wearing a Ranger top in a red car.
He was subsequently assaulted by the man who made off down Castlegreen Street in his vehicle.
Following the incident, the victim went to the Royal Alexandra Hospital where he received treatment for a facial injury.
The suspect is described as five foot six inches to five foot eight inches in height, average build and with short dark hair.
At the time of the incident, he was wearing a blue Rangers top, black shorts, and was carrying a black rucksack.
Police Scotland is now urging anyone who has any information on the incident to come forward.
Detective Constable Mark Gillies from Clydebank CID said: “I am appealing for anyone who may have witnessed this incident to please come forward.
“In particular I would like to speak to any motorists who were on Glasgow Road at the time, and may have dash-cam footage which could be of significance.
“Anyone with information is asked to contact Clydebank CID through 101, quoting incident number 3078 of Wednesday, 2 June. Alternatively you can call Crimestoppers anonymously on 0800 555 111.”