Although Haira did not throw the punch that put Mr Fisher on the ground, he "punched, kicked and stomped" him on his face while he was down.
As a result, Mr Fisher suffered brain damage and fractures to his eye sockets, nose, cheeks and mouth and was later told he had died twice and was resuscitated at the scene.
Mr Fisher was taken to Wellington Hospital where he was admitted to intensive care unit and kept in an induced coma for three days.
He later underwent facial reconstruction, which left him with titanium plates under both eyes and his top lip.
Mr Fisher spent weeks doing intensive physiotherapy for up to three hours every day, hoping to win back more movement and strength in his right arm and leg.
Mr Fisher's family were emotional as they read victim impact statements to the court today.
His father, Brian Fisher, said his family had been through a nightmare.
"Seeing one of my children in such a damaged state, something changed in me. At this day I still get emotional discussing it."
He later finished reading a statement from Mr Fisher's mother, Noeline, who broke down in tears while addressing the court.
Mr Fisher's brother Paul told the court he could not convey in words the pain his family had suffered and still endured.
He said his brother suffered from the effects of the attack to this day.
"Every time I see Peter these days, every time my emotions rise and have to be contained... [he is] physically slower, walks with a limp and is less coordinated."
Crown prosecutor Kate Feltham told the court that Mr Fisher was a "vulnerable victim" as he was down after the first hit.
"This was mindless, gratuitous violence and one with very serious consequences for the victim."
However defence lawyer Michael Bott said Haira was acting in self defence, and the attack was not pre-meditated, "but was a response to being approached by a large man wielding a hammer".
A statement from Haira that was read to the court said: "I acknowledge that Mr Fisher has suffered a tragedy that has changed his life, I feel for him every day, there are no winners in this."
Judge Davidson said it was clear the event had had a significant impact on Mr Fisher and his family.
"To say that the victim has been badly affected is really an understatement.
"He has suffered physically, emotionally and financially both in the shorter and longer term."