SINGAPORE - A group of students was alighting from a bus in the Orchard area one evening in January when one of them deliberately bumped a fellow passenger on his way to the exit. The resulting confrontation at the rear of the vehicle escalated into a full-blown assault by the group on the 18-year-old, leaving him with injuries including a bloodied nose and a cut lip.

On Monday, Gordon Chiw Xu Zhuo, 17, was sentenced to 15 months of probation after pleading guilty to being part of an unlawful assembly, and one other unrelated charge. He was also ordered to perform 130 hours of community service, and his parents have to sign a $5,000 bond to ensure his good behaviour. Three other youths - Leow Fa Dong, 20, Kek Wei Jie, 19 and Ee Kok Soon, 18 - had received the same punishment over the incident. The case against a fourth, Chai Zeping, 16, is pending.

A community court heard that on Jan 13, the group had boarded SBS bus 518 along Tampines Avenue 7 and sat at the rear. Their victim, Mr Nelsis Ong Wei Hua, 18, got on later with a friend and stood in the aisle near them.

At about 7pm, the bus arrived at the group's destination in front of Far East Plaza along Scotts Road. As Leow made his way to the exit, he intentionally bumped Mr Ong's back with his shoulder, causing the victim to push back in response. Kek, Chai and Chiw, who were about to alight, saw the pushing and shouting match that resulted. They returned to the rear and punched their victim in the head and body. Ee kneed the victim in the face when he fell forward. A sixth member of the group, Mr Marshall Low Jun Ming, 19, had already alighted. He reboarded the bus and broke up the fight.

For being part of an unlawful assembly to voluntarily cause hurt, Chiw could have been jailed for up to two years and fined.