It took Darryl Nicholson a day and-a-half to die from a single punch to the head, the High Court in Auckland has been told.
Israel Te Amo has denied the manslaughter of Darryl Nicholson, who died after the two came across each other on a street in Orakei back in February 2012.
The court was told Mr Nicholson insulted Mr Te Amo and Mr Te Amo responded by punching him in the jaw.
Crown prosecutor John Dixon said Mr Te Amo had to be held back by his friend to stop the fight continuing.
Mr Dixon said there was evidence Mr Te Amo took Mr Nicholson's shoes and cap, and that might have been the end of it if Mr Nicholson had not died a day and-a-half later.
The punch had caused bleeding inside the 35-year-old's head and his flatmates found him dead in his bedroom.
Mr Dixon said it was Mr Te Amo's punch which led to Mr Nicholson's death.
But Mr Te Amo's lawyer, Belinda Sellars, said Mr Nicholson had a knack of getting into fights and only a week before he died had been involved in another fight.
On that occasion his jaw was broken and he spent days in hospital.
Mrs Sellars asked the jurors if they could be sure of Mr Nicholson's movements and whether the fight with Mr Te Amo was the last one Mr Nicholson had.
She said her client was just 16 when he punched Mr Nicholson.
Ms Sellars asked the jury if they could really be sure it was that punch that caused Mr Nicholson's death.
She said brain injuries were complex, and the Crown's expert witness had over-simplified the evidence.
The trial has been set down for two weeks, with evidence expected to be heard from more than 20 witnesses.