Brody Colin Lohrey, 24, pleaded guilty to assault at the function at the Riverside Golf Club on November 16, 2019.

The court heard that Lohrey believed the 51-year-old complainant had made a disparaging remark about the fiance of his friend who was the intended groom.

Justice Robert Pearce said the single punch to the man's head occurred late in the evening after Lohrey had consumed alcohol.

The man fell to the ground with a bleeding nose and was taken to the Launceston General Hospital before being transferred to the Royal Hobart Hospital.

"The complainant was seriously injured with a fractured jaw, a skull fracture and subdural haemorrhaging," he said.

"A single punch rendered him unconscious and it is more likely that the fall caused the skull fracture."

The man was in hospital for two days but the court heard that he would make a full recovery.

Justice Pearce said Lohrey told police of his belief that the man had made an offensive remark about the woman to be married.

But he said when Lohrey approached the man he denied it and he was ushered away.

"You approached again and you now accept that no force was necessary and or that it was excessive and unjustified response," he said.

He said he accepted that Lohrey had not intended to cause such a serious injury.

He said that because Lohrey had not been in serious trouble before and had a good industrial record a period of imprisonment was not necessary.