Alo Ngata, 29, died in police custody on Wednesday morning after an altercation in the central suburb of Freemans Bay on Sunday.
Police tasered and restrained him after witnessing him attacking an elderly man, Superintendent Karyn Malthus said.
The friend, who did not wish to be named, met Ngata when the pair were studying at Tangaroa College in Ōtara.
He described the 29-year-old as "fiercely loyal" and coming from a large family.
"I saw him just a couple of months ago in town and he was still just the same humble as guy I knew in school."
The friend said he was not aware of any mental health issues, and had no idea why Ngata would have allegedly assaulted the man or resisted arrest.
"It's just such a surprise. As far as I know he didn't do drugs or anything. I just can't figure out what was going on that night."
Malthus said police were called to Beresford St on Sunday where they found Ngata attacking the man.
She said Ngata would not engage with the police and instead went towards officers in a "threatening manner".
Two officers then tasered him, Malthus said.
"The first two tasers were ineffective, the second two tasers from the other officer were effective and did bring the man to the ground."
Police arrested Ngata and he was handcuffed, restrained at the feet, and placed in a spit hood to prevent him from spitting at officers.
He was then transported to the Auckland police custody unit where he "continued to resist police", Malthus said.
However, he began to deteriorate while in custody. He was given CPR and transferred to hospital but died on Wednesday morning.
Malthus said she had reviewed footage from the police Eagle helicopter, which was first to arrive at the scene.
"What we can see there and what the Eagle staff were witnessing was [Ngata] assaulting the elderly man," she said.
Ngata struck the elderly victim to the ground and kicked him in the head "five or six times, possibly more and basically he kicked him unconscious", Malthus said.
Friends and family members have taken to Facebook to ask for "respect" for Ngata's family following the death.
Family members described him as a "family man with a big heart".
According to his Facebook profile, he studied product design at Unitec.
Ngata's family and friends were gathering at his home in Papatoetoe, south Auckland on Thursday night. They declined to comment when approached by Stuff.
Malthus defended the police's actions, saying it was normal practice for someone who had been tasered to be taken to the police station before getting medical treatment.
Situations like these were "volatile" and "high risk", she said.
"I have no doubt that if our officers had not intervened with the necessary tactical options they would have incurred serious injury themselves," she said.
Ngata was not "significantly known" to police, Malthus said.
Ngata's aunt Kristina Sofele told 1 News she understood her nephew's heart stopped while he was at the police station.
"We want to know as a family, how did that happen?" she said.
"We were initially upset about this whole thing and we had a lot of anger towards the police, but ... we've been talking with the police and they've helped us to understand what had happened."
The elderly man remains in a serious condition in hospital.