An incident that day between the victim and Kelly's son had prompted that action, the judge said.
"You [Kelly] then reached up and grabbed the victim by his clothing ... the victim fell through the doorway and landed on a concrete path, you then leaned over the victim, who was on the ground, and began punching him in the head.
"The [police] summary of facts states you punched the victim, with your right hand, an unknown number of times until your hand began to hurt ... you then switched hands and began punching with your left hand.
"You told him that if he touched your son again you would kill him," Judge Hastings said.
According to the summary of facts, Kelly then grabbed the victim by the throat and shook his head, which caused the back of his head to bang against the concrete. By this time the victim had been rendered unconscious.
Kelly disputed those facts.
The man was left with a cut to his forehead, a large gash, bruising and swelling to his left eye and grazing to his knees and chest. He was taken to hospital for observation.
Kelly admitted to police what he had done and said he was angry because the man had hit his son.
In a victim-impact statement, read by Judge Hastings, the victim said he was grateful his two boys had not been home to witness the assault.
The judge told Kelly: "There is some history between your boy and his boy; the victim says you are the father of a boy who bullies his son."
Judge Hastings said that according to a probation report Kelly had no remorse. Kelly acknowledged that from the dock.
He was sentenced to four months' home detention.
