The teen continued to swear at police and challenged an officer to a fight.
"F**k the Police, I'll take you on one on one," he yelled.
The teen was warned again that if he did not move on he would be arrested for disorderly behaviour.
Police later said that the teen's behaviour caused the others in the group to "become aggressive and obstructive and advance towards us in a threatening manner".
The officers feared for their safety.
They warned the teen once more - leave or get pepper sprayed.
The teen responded: "I'll f****** take you on pig".
He then advanced on police and was pepper sprayed in the face.
"When he was pepper sprayed, [he] fell to the ground," said Judge Doherty.
"[The officer] told [him] to stay on the ground, and put his hands behind his back.
"Initially [the teen] put one hand behind his back, however when [the officer] attempted to handcuff him, he reacted violently, pulling his arm away."
The teenager got up and charged at the officer, swinging his fists.
The other members of the group had become more agitated by this point.
Another officer pointed his Taser at the teenager and warned "50,000 volts, calm down".
"This had no apparent effect on the teen who responded 'I don't give a f***'."
TaserCam footage shows the teen wrapping his shirt around his wrist, with his fists raised in a fighting stance and a red "Bloods" bandanna tucked into the front of his trousers.
Two other people were pepper sprayed during the fracas for "exhibiting assaultive and threatening behaviour".
On the ground the teenager swung punches and continued to "thrash around".
One of the officers made the decision to Taser him.
The first discharge of the weapon missed the teenager and the officer took another shot which connected.
Judge Doherty said the officer who fired "was certain" that the teen's "grievously assaultive" behaviour would continue.
He thought the initial discharge had worn off and noted the teen's aggressive behaviour had not changed.
"He said that to neutralise the threat in the least violent way, while keeping himself and [the other officer] safe, he re-energised the Taser for a one second burst.
The teenager was later charged with resisting police, assaulting police, and disorderly behaviour.
He received diversion on all three charges.
Police notified the IPCA of the incident in July last year after TaserCam footage had been fully reviewed.
The authority concluded that the police officer's use of pepper spray was justified, as was the initial tasering of the man.
However, Judge Doherty ruled that once the man was on the ground, he was not in a position to pose an immediate threat.
"Therefore the officer was not justified in re-energising the Taser," his report stated.
"After using a Taser on someone, police should provide a reasonable opportunity for that person to surrender and obey their instructions before they use further force," said Judge Doherty.
"[The man] was not given that opportunity."
Auckland City Police District Commander Superintendent Karyn Malthus acknowledged the IPCA findings.
"Police accept the IPCA's findings that the officer was unjustified in discharging his Taser a second time on the same male," she said.
"This was an extremely dangerous situation where police officers, who were outnumbered by a large group with a number of aggressive males, were forced to take immediate action due to fears for their own safety," she said.
"Our police officers are put in high-pressure situations on a daily basis where they are forced to make quick decisions, often in the face of danger.
"While we accept the IPCA's criticism of the additional discharge of the taser while the offender was on the ground, it is important to view this in the context of what was an extremely volatile situation where the officer, who anticipated the offender getting up to attack, was having to make a quick judgment decision to ensure his safety and the safety of his colleague.
"It is also important to recognise that the IPCA found the officers were justified in the use of pepper spray and the initial use of the Taser.
"The IPCA report also found police staff ensured the appropriate medical assistance was provided to all three males involved."
