Darren Donel Roche (39) entered Costcutter in Snow Hill, approached his victim from behind and repeatedly punched him in the head and face.
The assault, which happened at 7.20 pm on 19 December, left the man on the floor, with bruising and swelling to the face and a cut beneath his eye.
Roche, who has lived in Jersey for ten years, fled the scene moments after the attack, the Magistrate’s Court heard.
During a police interview, the defendant said that he had committed the assault because he was told the man had threatened to ‘stab his god-daughter in the head’.
After viewing the CCTV footage of the incident, Roche told officers that he had been drinking since 11 am on the day of the attack and that he did not know what had come over him when he entered the shop.
Relief Magistrate David Le Cornu said that he believed the victim’s injuries were ‘serious’ and that the offence had been aggravated because it had taken place in front of shoppers and children.
Mr Le Cornu added that he was prepared to grant a non-custodial sentence, but that the defendant was ‘very, very lucky’ to have avoided jail.
Roche was sentenced to 180 hours of community service and ordered to pay £500 compensation to his victim. He was also banned from entering licensed premises for a year.
