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Robinson has admitted a charge of injuring with intent to injure for the attack which witnesses said left a man unconscious and bleeding outside the Palace Hotel in Te Aroha.
His lawyer Moana Dorset said Robinson was "really bummed" and took full responsibility for the attack.
Robinson will reappear in the Hamilton District Court next month for sentencing.
The attack happened after a group of around 50 men had been on a "man-cave" tour of several properties around Te Aroha on December 9.
Facebook pictures on the Palace bar's website show the group in a large bus, all dressed in black singlets, touring homes where they played poker, threw kegs of beer around a lawn and drank beer through a funnel, played drinking games and shot guns before returning to the Palace Hotel.
The website described the outing as a "man cave tour".
After they returned to the Palace Hotel, Robinson, a 1.97m, 116kg former rugby player, became involved in a verbal altercation with a much smaller, older man.
The man was said to be about 1.65m and about 50 years old.
A witness said Robinson pushed the man and punched him in the face. Robinson is also accused of throwing full bottles at the man, a Te Aroha local, as he tried to leave the bar.
Robinson appeared in the Hamilton District Court on December 20. He is due to reappear on January 29.
Dorset last night said: "He's sorry, he's really bummed about what happened. If he could take it all back he would. He told police he would plead guilty at the first opportunity and that's what he did."
Yesterday, many Te Aroha residents closed ranks and refused to talk about the incident involving the town's most famous son.
One said: "When [Robinson] isn't drinking and he's straight, he's all good."
Two local men who knew Robinson from his involvement with the local rugby team said: "Once he has had a couple of beers in him he gets really competitive."
An acquaintance of the man who was attacked said that he had suffered facial injuries, but was making a good recovery. "He's a nice guy, he didn't deserve that."
Nobody was home at Robinson's 1.4ha lifestyle block just outside Morrinsville yesterday. A neighbour said he had gone fishing off the Coromandel. A real estate sign listed the property as for sale.
The sign said the property included "a lockup shed that includes a "games room/man cave".
The 36-year-old earned a reputation as a fearsome enforcer on the rugby field, and played the last of his 12 tests in the 2007 Rugby World Cup quarter-final defeat to France.
Robinson was also a member of the local pig hunting club.