However, supermarket staff and other members of the public stepped in to stop the assault.
The detective praised their “brave intervention”.
“If it’s not for this action, the offender’s cowardly act could have resulted in a far worse outcome.”
Richards said the man, who was taken to hospital, was left shaken but was recovering.
Police were “following good lines of inquiry” and had examined CCTV footage of the incident.
“This is an appalling display of violence and it has no place in our community,” Richards said.
Police were determined to hold those responsible to account and called on the public with any information to come forward.
People can contact police on 105, quoting file number 231120/9056, or anonymously via Crime Stoppers on 0800 555 111.