David Bernard was leaving a cafe on his way to the Bilston outdoor market where he runs a carpet shop when he spotted Luke Dhear who said to him: "You called the coppers," Wolverhampton Crown Court was told.
Bernard, 59, picked up a five foot long metal bar and swung it as he passed Mr Dhear, hitting him once.
Mr Simon Rippon, prosecuting, said: "It struck him full on the back of the head and he felt blood going down his neck and back. He also felt dizzy."
Mr Dhear was taken to New Cross Hospital where injuries to his head and a hand were treated. Fortunately neither was very serious.
Bernard told police that he closed his eyes when swinging the bar but accepted it could have caused far more damage to the person he hit.
Mr Rippon told the court: "There is something he and the victim had in common which is they both agree that Mr Dhear said 'You called the coppers' before being struck by the bar."
Mr Gerry Bermingham, defending Bernard, explained: "He did not like being called a snitch. He reported to the police that his phone and bank cards had been stolen and mentioned the name of the person he thought was responsible."
He added: "The defendant is a popular and well regarded man with a shop in Bilston open market. He has built up a little business which is doing reasonably well but has also been suffering significant trauma for reasons that will not be made public."
Bernard, of Wellington Road, Bilston, admitted causing grievous bodily harm on May 23 and was given a ten-month jail term, suspended for two years, with £250 costs.
Recorder David Mason QC told him: "There was an element of provocation and a background to what caused you to act completely out of character. I have read a lot of positive things about you from friends and workmates. You have also had to suffer sad personal circumstances."