Armstrong Renata then came from behind and punched the 18-year-old in the head, causing massive brain trauma. He died in hospital the next day.

Armstrong Renata (pictured) pleaded guilty to killing Cole Miller with unlawful striking causing death. Credit:Facebook

Renata, 22, pleaded guilty in the Brisbane Magistrates Court on Wednesday to unlawful striking causing death. He will be sentenced in the Supreme Court later this year.

A second man is still facing charges over Mr Miller's death.

Mr Miller was an elite water polo player and had been on track to follow in the footsteps of his brother Billy, who was part of the Australian men's team at the London 2012 Olympics.