Two other men also faced charges in relation to this incident: David Dean Lawson also pleaded guilty to the same charge and will be sentenced in May, while Shannon Withers was found not guilty of the stabbing after a jury trial last week.
Mrs Terrill said in the proceedings yesterday her son, who was using clothing which included a Mangu Kaha T-shirt on the day of the incident, was not a gang member.
She told the court her son had disabilities as a result of a childhood trauma and he struggled to identify wrong situations or when people were trying to take advantage of him.
He was using the clothing which was given to him as a present after he helped save the life of someone else, she said.
"He is vulnerable to being used by others because of this disability.
"He thought they were friends because they were nice to him — and Philip did not understand the full implications of this friendship."
She said since February 16, 2018 - when Mr O'Brien was punched and stabbed by a group of eight to 10 Mongrel Mob members in Janet St, Invercargill - her son had been dealing with anxiety, stress and depression.
The incident occurred when O'Brien was walking with three other people on Ythan St near Janet St when three vehicles intercepted the group.
A group of 10 people, who were recognised as Mongrel Mob members or associates, then approached Mr O'Brien and started to beat him on the ground while pulling his clothes off.
The summary of facts says the victim was stabbed five times in the lower back, causing life-threatening injuries, which included lacerations to his liver, kidney and spleen.
Defence lawyer Sarah Saunderson-Warner said her client was not the one who stabbed O'Brien. She said he had a secondary party liability — his van was identified as one of the vehicles at the scene of the offence and Tauroa had told the police no one else had driven it.
"He is not the primary offender," she said.
Justice Nation said Tauroa had to accept responsibility as chapter president.
During the proceedings, he said Tauroa had 31 convictions in 23 years.
"The fact you did not wield the knife does not lower your culpability.
"You assisted in the attack of what it could have killed a 23-year-old man that was doing nothing to you or anyone else."
However, to sentence him, Justice Nation considered a cultural report on Tauroa.
The document says Tauroa was son of a gang member and grew up in an environment of violence and abuse.
"You had a early exposure to gang life and violence. You have witnessed and experienced horrific physical and emotional abuse through your child hood and adolescence."
The reports says Tauroa tried to keep his family and gang life separated and he did not wish his children to follow the gang pathway as he did.
Justice Nation believed his background had significant impact in Tauroa link to gang and in the offence; he gave Tauroa 15 per cent of discount on the sentence due to "personal mitigations effect".
"You need to understand it is a merciful approach. You are in an age where you must be responsible for the choices you have maid in your life."
Justice Nation also gave 20 per cent of discount for an early guilty plea and sentenced him to 6 years and 9 months in prison.
He said if Tauroa returned to court, he would not expect the same kind of discounts.
