A teenager has told a coroner's inquest how he tried in vain to protect his rugby teammate as two boys attacked him.

The inquiry into the death of 15-year-old West Auckland schoolboy Stephen Dudley began at Auckland District Court this morning.

A witness, who cannot be named, said he tried to stop a fight after a rugby practice on June 6, 2013.

While he held Stephen back from a potential brawl with another teen, an older boy intervened.


"[He] came around behind us and using a closed fist punched Stephen in the right side of the neck," the witness said.

"He used heaps of force, because Stephen fell into me." As the victim slumped, the boy supported him.

"I was holding Stephen up and saw the [two boys] coming towards us. I knew they were going to keep punching him so I turned his head," the witness said.

"[They] kept punching him in the side of the body; I don't remember how many times. I was trying to push them back with both hands so their punches weren't as hard."

As he let go, he said, Stephen slumped to the ground and the two attackers "walked off casually".

Another teen witness, who filmed the fight on an electronic device, gave a slightly different account.

He said the older boy shoulder charged Stephen, connecting with his jaw and flooring him.

While the victim was on the floor he said the assailants punched him in the back, about three times each.

"He was covering his face, trying to protect himself," the witness said.

The boys walked away, he told the court, and Stephen "seemed fine".

But the teenager said he collapsed shortly afterwards and some of the boys started CPR while they waited for an ambulance.

One of them, 18 at the time and whose name is permanently suppressed, was discharged without conviction in the High Court at Auckland in 2014 after a manslaughter charge was dropped to one of assault with intent to injure.

His co-defendant - 16-years-old at the time - also admitted assaulting Stephen and was similarly discharged without conviction three months earlier.

The schoolboy died after paramedics rushed him to hospital.

Medical examinations showed an undiagnosed heart condition contributed to Stephen's death, which was critical to the prosecution dropping the manslaughter charge.

The victim's parents were devastated by the court's decision to release the teenagers without consequence.

"He was a lot smaller than you and you attacked our son from behind. He had no idea about the attack he was to be subjected to," father Brent Dudley said at the sentencing hearing.

"Any thoughts of forgiveness are out of the question at this stage. I hold you entirely responsible for the death of our son ... you own that."

The inquiry before Coroner Gordon Matenga is scheduled to last all week.