Police believed a dispute between two parties escalated into more serious violence.
It was believed a man lay injured on the front lawn of an empty house for more than an hour before about six AOS members carried him out on a stretcher.
The injured man was transported to the Whangarei Hospital in a stable condition.
Whaanga initially appeared in the Whangarei District Court and was remanded to appear in the High Court for a bail application.
In the High Court on Tuesday, Whaanga had a discussion with his lawyer, Catherine Cull, before returning to court and said he would plead guilty.
Those who turned up for jury selection were then excused.
Whaanga was remanded on bail to reappear for sentencing on December 12.