The extent of his injuries is not known, but he was transferred to hospital for further treatment.
A hammer has been recovered for forensic examination and CCTV investigations are continuing, a force spokesperson said.
An eyewitness told BlackCountryLive that the busy store was evacuated in the aftermath of the drama, triggering panic.
“It was horrible,” they said. “The man was stuck across the head in front of children.
“All the premises were evacuated and police and ambulance personnel ran in to help him.
“I hope he’s okay. ”
A West Midlands Police spokesperson said: ‘We were called to The Range, Longacres, Willenhall shortly before 2pm today (11 October) following reports that a man was beaten with a hammer during a fight.
“A man in his thirties suffered a head injury and was taken to hospital. The extent of his injuries is unclear at this point.
“A hammer was recovered for forensic examination and CCTV investigations are ongoing.
“Anyone with information can contact us through live chat on our website or by calling 101. Please quote the 1972 journal number of 10/11. “