A pair of twins ganged up on a policeman as they "did not like the victim's face" and rained blows on him, causing a traumatic head injury.

Sergeant Chong Jiawei, 27, suffered multiple facial injuries and was given 29 days of hospitalisation leave after the unprovoked attack.

One of his attackers, Muhammad Farhan Jaffri, also assaulted a second policeman and abused a policewoman with vulgar language.

Farhan, a 27-year-old Singaporean, was sentenced yesterday to 33 months and four weeks' jail, three strokes of the cane, and a fine of $3,500. He pleaded guilty to causing grievous hurt to Sgt Chong and causing hurt to the officer's colleague, Reservist Sgt Muhammad Irfan Misran, 22.

Farhan also admitted to abusing Staff Sgt Tity Sumarni Abd Ghani, 35, with vulgar language, vandalising a police Land Rover, and being a secret society member.

The case involving his twin brother, Muhammad Fiqkri Jaffri, is still pending.

On Feb 23 last year, Farhan and his wife had an argument at the void deck of Block 755 Jurong West Street 74 around 4am and police were alerted to the commotion.

Officers arrived at the scene and Staff Sgt Sumarni asked the couple if they were all right.

Instead of answering, Farhan behaved defensively and his twin brother turned up soon after.

Deputy Public Prosecutor Chng Luey Chi said Fiqkri behaved aggressively and demanded to know why they were questioning the accused.

Farhan then abused Staff Sgt Sumarni with vulgar language and left the scene, only to return minutes later.

Fiqkri asked his brother "which police officer's face he did not like" and Farhan responded by gesturing at Sgt Chong. The two siblings then assaulted the policeman and continued raining blows on him after he fell to the ground.

When the other police officers stepped in, Farhan assaulted Sgt Irfan, who managed to drag him away with the help of his colleague, Sgt Charmaine Tan, 27.

The court heard Staff Sgt Sumarni had to use her baton to hit Fiqkri when he continued attacking Sgt Chong. Fiqkri was later restrained and handcuffed.

Meanwhile, Farhan was escorted to a police Land Rover and while seated in the rear, he kicked one of the vehicle's windows three times, causing it to shatter.

Separately, the court heard that Farhan has been a secret society member since 2007.