SINGAPORE - Unhappy with his younger sister's former boyfriend, Zulkirman Hassim Abdullah,21, decided to confront the man last September, a court heard on Thursday.
He went to a pavilion behind Block 360 Corporation Drive, together with two others, after friends told them that the man they were looking for was there.
Zulkirman told the man, Mr Mohammad Khairul Nizam Misran, 24, that he was unhappy with him for having sexual relations with his sister.
He then punched him twice in the face and the arm.
Zulkirman's friends, Nur Fazli Mohd Ghazali, 29, and Shahrul Samsudin, 21, then joined in the fray, punching and kicking their victim.
Wanting to humiliate him further, Zulkirman asked Mr Khairul Nizam to choose whether he wanted to strip or to keep getting beaten.
After the victim got undressed, Zulkirman forced him to masturbate .
Zulkirman and Shahrul continued to rain blows on Mr Khairul Nizam later, after he got dressed.
When the assaulters left, the victim went to the National University Hospital.
His left cheekbone was fractured and a part of his face was swollen.
Nur Fazli also made off with Mr Khairul Nizam's Samsung Galaxy Ace mobile phone.
On Thursday, Nur Fazli was jailed 12 months for his role in the attack, after pleading guilty to one count of voluntarily causing grievous hurt.
Another count of voluntarily causing hurt and of dishonest misappropriation of property were taken into consideration in sentencing.
In mitigation, Nur Fazli's lawyer Johan Ismail said the assaulters thought that Mr Khairul Nizam had sexually assaulted Zulkirman's sister, although the prosecution said there was no such evidence.
The lawyer added that Mr Khairul Nizam told the group he "felt dirty" with Zulkirman's sister.
Shahrul also received a 12-month jail term in March.
Zulkirman's case is before the courts.
For voluntarily causing grievous hurt, Nur Fazli could have been jailed for 10 years, and fined or caned.