A man armed with a machete went into a Weston-super-Mare supermarket and hit a shopper in the head.
The incident, which happened on Sunday, saw a man holding a machete chase another unknown man into Tesco Express in Severn Road.
A 46-year-old man and a woman intervened, with the man hit in the head and taken to hospital.
Three men aged 54, 39 and 32 were arrested following the incident and the machete seized by police.
The 54-year-old man has been released under investigation, while the other two men were released without charge.
A police spokesman said: "We were called to Tesco in Severn Road at about 7.30pm on Sunday following reports an unknown man had been chased into the store by a second man armed with a machete.
"The man who intervened was hit around the head with the machete and needed hospital treatment for a cut.
"The man originally being chased and the suspect both left before police arrived.
"Anyone with information which could help the investigation is asked to get in touch through our website, or by calling 101, quoting reference 5219207376."
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