A man bragged to his friends after he elbowed a man in the head, knocking him unconscious, fracturing his skull and causing a brain bleed.
Judge Walker said MacGregor had consumed a large quantity of alcohol on a night out with his brother and other friends.
Counsel Keith Owen said an altercation had gone on in the shop, prior to the assault, between MacGregor’s brother and the victim.
"He [MacGregor] went and tried to break it up and pushed the victim away."
He then left the shop expecting his brother to follow.
It was when MacGregor returned to the shop "his elbow connected with the face of the victim", Mr Owen said.
However, police did not agree with MacGregor’s account of events.
Sergeant Penny Stratford said police believed there was no apparent reason MacGregor had pushed the victim forcefully in the face with his right elbow.
Judge Russell Walker said the victim fell to the ground on impact and remained unconscious for one and a-half to two minutes.
"You then walked outside of the store without making any attempt to assess the victim," the judge said.
CCTV cameras in Queenstown captured MacGregor demonstrating to his friends how he had attacked the victim.
As a result of the attack, the victim suffered a fractured skull and a brain bleed.
He was transferred to Christchurch Hospital by helicopter and was in the intensive care unit for two days.
As a result of the attack had been unable to drive for several weeks, he could not stand up for long periods of time and was unable to work for 24 weeks.
"This was a serious unprovoked incident of serious violence," Judge Walker said.
"Although not extreme violence, the victim did not see it coming."
Judge Walker said this was an all-too-common incident in Queenstown.
"Young men who cannot control their anger while out drinking.
"The difference between punching someone and causing a serious injury as you did, or causing death is often down to sheer luck."
Judge Walker sentenced MacGregor to eight months’ home detention and ordered him to pay emotional harm reparation of $7000.
