The victim was forced to the ground and repeatedly punched and kicked during the assault, which left him needing hospital treatment.
Police today released details of the attack, which happened in Westwood between 2am and 3am on on Sunday, June 4.
It happened moments after the victim tried to intervene in what was described as a "domestic related incident".
The victim suffered facial and torso injuries and was taken to hospital by ambulance, where he was treated for the broken collar bone.
Three men and a woman are believed to have been involved in the incident.
A North Yorkshire Police spokesman said: "We are conducting enquiries and are particularly keen to speak to anyone who may have witnessed a verbal altercation between a male and female on Pavilion Terrace, Scarborough or witnessed the assault that followed."
The suspect is described as a white man in his early to mid 20s, if medium build with broad shoulders and around 5ft 10in.
He is described as having short dark hair, shaven on the sides and longer on the top.
The suspect was described as wearing a dark coloured T-shirt in a V-neck style with long sleeves and grey cotton tracksuit bottoms.
Following the assault, he ran off across the car park at the rear of Poundstretcher on Westwood.
Anyone with information is asked to call police on 101, select option 2, and ask for Matt Smout.
Information can also be passed to Crimestoppers anonymously on 0800 555 111.
Quote the North Yorkshire Police reference number NYP04062017-0092