The incident happened on London Road near the junction with Beresford Road, on Saturday 18 September 2021.
At around 4pm, a man in his 40s was approached by a group of young men he did not know, who were riding mopeds.
It is alleged the group assaulted the man with weapons including a baseball bat, causing serious bruising.
Investigating officer, Detective Constable Martin Stevens, said: ‘There were several people in the area at the time and we are urging anyone with information, or mobile phone footage of the incident, to contact us.
‘Two of the suspects are described as having dark coats and were wearing black motorcycle helmets. A third, who was a passenger on one of the mopeds, was white with short dark hair and was not wearing a helmet.’
Our detectives are appealing for any witnesses who have not yet spoken to us to contact the appeal line on 01474 366149, quoting reference 46/813433/21.
Motorists with dashcam and residents with doorbell CCTV, are also asked to check for footage that may assist the investigation.