A 17-year-old schoolboy who got mixed up with a youth street gang is in custody awaiting sentence for a street bashing and robbery in Christchurch.

The YSK gang attacked two men as they walked beneath the Lincoln Road overbridge at 2am on Sunday April 18.

Defence counsel Kerry Cook said that year 13 student Tuari Damyn Karipa-Rangi was from Tokoroa and was not a member of the gang, Christchurch's Court News website.

But he apparently became associated with the gang during his holiday in Christchurch and was one of two youths who did the bashing with pieces of wood.

Police say YSK stands for Young Skuxx Klicxx and the gang has between 10 and 20 members.

Police today withdrew serious assault charges against Karipa-Rangi and replaced them with one aggravated robbery charge. He pleaded guilty to the charge of robbery with four other named people, and more unknown associates.

Some of the group have been appearing in the Youth Court.

Christchurch District Court Judge Colin Doherty said it was virtually inevitable that Karipa-Rangi would be jailed and refused bail for the remand before sentence on September 4.

He asked for a pre-sentence report and victim impact reports from the two victims, who ended cut, bruised, and one of them was admitted to hospital.

Mr Cook said there were significant mitigating factors to be taken into account, and Karipa-Rangi's sentence could still fall within the range where home detention could be considered. He had been on a 24-hour curfew on bail since his arrest and there had been no breaches.

Karipa-Rangi was doing well at school and the school work had been sent to him to continue his studies while on bail in Christchurch.

The youth had a large group of family and supporters in court, and several were crying when he was locked up.

One of the victims in the assault was attacked by a youth with a cricket wicket, and kicked and punched by members of the group. He got to a traffic island in the middle of Lincoln Road, where he was knocked unconscious. When he woke up his watch, passport, and wallet were missing.

The other victim was hit on the head from behind, and punched in the face and had his wallet taken.

One victim had a suspected broken jaw, lumps, bruising, and a cut to his forehead that needed five stitches. He was admitted to hospital. The other victim had cuts and bruises.