A 19-year-old restaurant helper saw a couple fighting outside Golden Mile Complex and told the husband to stop pulling his wife's hair.
That led to another quarrel with the teen, Nikthik Al Sial, kicking and punching the 42-year-old man several times in the face, breaking his nose and an eye socket.
Yesterday, Nikthik, a Malaysian, was jailed for six months after he pleaded guilty to one charge of causing grievous hurt.
It all started when the victim, Mr Goh Ah Heng, was seen chatting with an unknown woman outside Golden Mile Complex in Beach Road in the early hours of July 15.
Mr Goh's wife Kongkoet Wiphada, 33, had gone to a Thai disco there with a cousin and two friends. The four women left at about 5.10am, and saw Mr Goh and the unknown woman.
Mr Goh's wife confronted him and the couple had an argument.
When Mr Goh pulled his wife's hair, her cousin and friends tried to break up the fight, but to no avail.
Nikthik heard Ms Kongkoet's cries for help and intervened. A fight broke out between the two and Nikthik kicked and punched Mr Goh in the face. Mr Goh fell backwards, hitting his head on the ground. Nikthik then kicked him twice in the face before fleeing.
Ms Kongkoet, her cousin and a friend took Mr Goh to Tan Tock Seng Hospital in a taxi, but he refused to alight when the cab got there. They then took him to a 24-hour clinic in Bedok.
Mr Goh was advised to go to a hospital, but went home at about 6.15am.
Around noon, he became unconscious and was taken to Changi General Hospital. His nasal bones were broken, as was his right eye socket. There was also bleeding in his brain. Mr Goh underwent emergency surgery and was discharged after 55 days in hospital.
The maximum punishment for causing grievous hurt is 10 years' jail and a fine and caning.