A plain clothes police officer was assaulted in Sainsbury's supermarket in North Walsham.
The officer, who was on duty, was punched and suffered a bloodied nose and swelling to both eyes.
A 15-year-old boy was arrested on suspicion of assaulting a police officer and questioned before being released under investigation while enquiries continue.
It happened at about 1.15pm on Sunday, June 25 when the victim approached a number of youths involved in a disturbance at the Bacton Road store.
Officers are keen to hear from anyone who may have witnessed the incident – witnesses should contact PC David Greenwood at Cromer police station on 101 or call Crimestoppers anonymously on 0800 555 111.
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