A 46-year-old man was arguing with a teenage boy outside the Wickes store in Reading Road, at about 3.40pm on Saturday (June 29).
The man was then approached by the boy's parents. The father punched him in the head twice and the mother kicked the victim's vehicle, causing significant damage to the front passenger door.
Investigating officer PC James Blowers from Loddon Valley police station said: "This was an unprovoked attack in broad daylight, right outside the main entrance to Wickes.
"There were a number of people in the car park and shop at the time so I am appealing for any witnesses who can provide further descriptions or more details about the vehicle involved."
The woman was white, aged 38 or 39, with long blonde hair tied into a pony tail. At the time of the offence, she was wearing a light pink top.
The man was white, around 5ft 7ins and of a very muscular build with a shaved or bald head.
He was wearing a light coloured top and trousers. They drove a new-looking gold or beige pickup truck.
Thames Valley Police is appealing for information about the incident.
Anyone with information can contact police on 101.
If you don't want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.