The man who punched Stephen Dudley has said he feels responsible for the teenager's death and has labelled himself a "coward".
The coroner's inquest into the death of high-school student Stephen Eruwera Dudley entered its third day at Auckland District Court today.
So far, the enquiry has heard from members of the victim's rugby team who said an argument between two teenagers led to a fight in the middle of a field on June 6, 2013.
There has been evidence of some pushing and swearing between the 15-year-olds but the situation became serious when an older boy - then 17 - entered the fracas and struck Stephen, despite other boys trying to hold him back.
He gave his account of the incident for the first time in court today.
"I punched him with my right fist. I don't remember much else of the fight because it happened so quickly," he said.
Witnesses said he and the other boy continued raining blows on Stephen as he lay on the floor, but he said he did not remember that.
"I've never thrown a punch in anger before and didn't realise how hard I'd punched Stephen, who fell to the ground. I thought I had knocked him out and got scared. I wanted to just get out of the whole situation," the now 20-year-old said.
"I feel like Stephen is dead because of me. Sometimes I think about what I could've done and what I should've done differently."
The man, who came back from playing sport overseas to give evidence, said he found it hard to talk about what had happened.
"I wish I'd just broken up the fight. Instead I made it worse. Using violence to deal with conflict was not the right thing to do. But I also feel really bad for not checking to see if Stephen was really ok. I was more concerned for myself and getting in trouble than I was for my schoolmate. I was a coward and I still feel ashamed when I think about it," he said.
"I've brought shame on my parents and my family. Most of all I'm sorry for the pain I now know Stephen's family must be feeling."
The 15-year-old collapsed as the two assailants walked away and an ambulance was called as he began frothing at the mouth.
Stephen later died in hospital and two teens were arrested and charged with manslaughter.
The older defendant was discharged without conviction at the High Court in Auckland in 2014 after the charge was dropped to one of assault with intent to injure.
His co-defendant also admitted assaulting Stephen and was similarly discharged without conviction three months earlier.
Medical examinations showed an undiagnosed heart condition contributed to Stephen's death, which was critical to the prosecution dropping the manslaughter charge.
Stephen's parents Mona and Brent are due to give evidence today.
The enquiry before Coroner Gordon Matenga is scheduled to last all week.