SINGAPORE - A 21-year-old man took part in a violent group attack on two victims last October, which left one with serious head injuries.

For rioting, Ahmad Ridhwan Wee Ahmad Jafni was sentenced to three years' jail and six strokes of the cane on Wednesday.

He and some others in a group of five had punched and kicked Mr Shawn Ho Yong Han, 25, and Mr Wang Jie Feng, 21, outside a club along Serangoon Road at about 3.30am on Oct 22 last year.

The assault left Mr Ho with a left skull fracture and brain injury. He also suffered post-traumatic epilepsy, and will need to take anti-convulsant medication for the rest of his life.

District Judge Shaiffudin Saruwan said he watched the National Geographic channel the night before, and said Ridhwan and his group behaved like a pack of hyenas.

The court heard that the victims met at Club Flux at Serangoon Road for drinks at about 11.30pm on Oct 21 last year. Ridhwan's group was also there for drinks.

Just before the two victims were about to leave at about 3.30am, a performing artiste came over to talk to Mr Ho.

A patron of the club who was allegedly sitting with Ridhwan's group was observed by Mr Wang to have pointed his finger aggressively at Mr Ho.

Sensing a possible confrontation, the victims left the club to catch a cab along Serangoon Road. They were followed by Ridhwan and his friends, who caught up with the duo and punched and kicked them for about two minutes.

Mr Ho was taken to Tan Tock Seng Hospital with cuts and head injuries. He was discharged two days later against medical advice.

He was transferred to Mount Elizabeth Novena Hospital, where a brain scan showed post-traumatic aphasia and bleeding in the brain. Mr Ho was initially unable to speak but has partially recovered. Mr Wang did not seek treatment for bruises.

Ridhwan has a previous conviction for loanshark harassment. He was released from reformative training in October 2013 and placed under supervision.

The judge said he was very concerned over the escalation of violence by young people, and more so with Ridhwan who had gone through reformative training.

Annual police statistics showed that 322 youths were arrested for rioting last year, 39 more than the 283 in 2013. In 2012, 239 youths were nabbed for rioting.

Judge Shaiffudin said he agreed with Deputy Public Prosecutor Jason Chua that deterrence is and should be dominant when deciding on Ridhwan's sentence.

He told Ridhwan he has a lot of time to reflect in prison, and hopes that the young man's promise to change is genuine. So far, only one of the other four has been sentenced to RTC, while the case against the rest is pending.

The maximum penalty for rioting is seven years and caning.