"No doubt he, visiting this country for the Rugby World Cup, thought you were just another easy-going Kiwi, he'd be safe to go off with," Judge John McDonald said.
Without warning, Tau punched the victim twice in the head, knocking him unconscious. One of Tau's friends fled but the other watched as he went through the victim's pockets, taking a cellphone and wallet. He also removed his watch.
Judge McDonald said it was fortunate someone found the victim lying unconscious on the road and called for help.
Tau was later found with the victim's cellphone in his pocket.
Mr Hosegood spent four days in hospital having teeth removed and metal plates inserted in his jaw.
"What he thought was going to be an enjoyable trip to this country of ours to watch a number of Rugby World Cup matches turned into horror because of what you did," Judge McDonald said.
Tau's thuggery would have a "ripple effect" on the region, which depended on tourism for jobs and income.
"When tourists decide to come to this country some of them will say, 'Well, we're not going to Paihia, we're not going to that Bay of Islands, we're not going further north, because if you go up there all that will happen to you is you will be bashed in the street by some thug'," he said.
Tau's attack on the English tourist was his second offence under three strikes legislation. If he is convicted of a third he will serve the maximum sentence, which, in the case of aggravated robbery, is 14 years.