The victim, who is in his 50s, was walking along the river path at the back of the recreation ground at around 5.30pm on Saturday (12/09) when he was attacked by a group of three males.
He was punched three times in the face and left with bruising.
The first suspect is described as white, around 17 to 20 years old, of slim build with dark hair. He had tattoos on his neck.
The second was also white, of similar age and build, and was quite tall.
The third, who was with the group but did not take part in the assault, was of stockier build with short fair hair.
PC Michelle Haley said: “We know there were a number of witnesses to the incident, including one man who intervened and threatened to call the police.
“If you saw what happened, or you believe you may recognise the descriptions of the suspects, then please call us.”
Anyone with information should call Wiltshire Police on 101, quoting crime reference 54200091959. Alternatively you can call Crimestoppers anonymously on 0800 555111.