Complainants Clifford Matoka and Damian Leota - of Samoan heritage - had been separated from a larger group earlier in the night and bumped into a group of eight or more Tongans, which included the Moala brothers.
Mr Shaw said there were differing accounts as to what the trigger was for the confrontation but it quickly turned violent.
Mr Matoka came off worst, sustaining concussion and significant blood loss after an artery was nicked, he said.
The Crown alleged the cuts were caused by a bottle.
"He was described as being on the ground with blood pouring away as blows continued to come," Mr Shaw said.
Security soon intervened and tried to drag the bloody Mr Matoka away from the scene but it is alleged George Moala continued the attack as the man was led downstairs.
He later told police he was "retaliating" after the man tried to punch his sister.
Mr Shaw said CCTV showed the action spill out on to the street before a police van turned up to round up those thought to be involved.
It showed George Moala attempting to flee the scene before being apprehended by police, he said.
The two complainants, as well as police and security guards, will give evidence and Mr Shaw said it would not be clear-cut as to exactly who did what.
"It's very difficult to get a blow-by-blow account in the melee with fists and feet flying," he said.
But he told the jury they could be sure the brothers played a significant role in the alleged offending.
George Moala, who has represented Tonga at under-20s level, signed a two-year contract with the Blues after an impressive season last year with the Auckland NPC team.
The trial, before Judge Rob Ronayne, is expected to last four days.
