SINGAPORE - A night of merrymaking went awry for three friends at a St James Power Station club in 2017 when they assaulted a plainclothes policeman who was on duty at the time.

District Judge Salina Ishak convicted the 25-year-old offenders on Wednesday (April 1) after a trial.

Coretta Leong Yin Teng, Lim Yang Horng and Marcus Goh Jun Fong were each found guilty of voluntarily causing hurt to Sergeant Tan You Chuen. Lim was also convicted of verbally abusing the officer with vulgar language.

The trio were at the Envy Dance Club in the wee hours of Nov 12, 2017, when a fight broke out on the dance floor. The trio and their friends then made their way to a table near the club's entrance.

The police were alerted and Sgt Tan arrived at the scene with his colleagues at around 4am.

During the trial, the policeman testified that he initially suspected that the trio and their friends were the ones who were involved in the fight and asked them about it.

He then told them to leave the club immediately if they were not involved in the brawl.

According to Sgt Tan, Lim then said: "Why should I leave the club?"

Sgt Tan replied that he was a police officer.

In his submissions, Deputy Public Prosecutor Houston Johannus said: "The reason Sgt Tan proffered for asking the accused persons' group to leave the club was for them to not complicate the situation further by going back to the dance floor - and there (was) a slight possibility that they might 'sandwich' his officers (there) - potentially causing his officers to get hurt while attending to the fight."

Sgt Tan had testified that as he was walking away, he heard somebody utter an expletive directed at the police. He added that he turned around to ask the group about what had been said and Lim responded by hurling vulgar words at him. A scuffle broke out soon after.

DPP Johannus said: "Lim throws the first punch at Sgt Tan. A struggle ensues between Sgt Tan and Lim. Lim does not dispute he had assaulted Sgt Tan by punching him at least three times and one of the punches caused Sgt Tan's spectacles to fly (off)."

Goh and Leong then joined the attack. Goh punched Sgt Tan's face at least once, while Leong forcefully grabbed the officer's neck.

The scuffle stopped when the club's bouncers and one of Sgt Tan's colleagues shone their torches at the offenders.

Sgt Tan went to Alexander Hospital's acute care clinic later that morning, and he was found to have a head injury. He was given two days of medical leave.

Leong and Goh were represented by lawyers Choo Zheng Xi, Low Ying Ning and Wong Thai Yong. Lim had engaged lawyer Evan Teo to represent him.

Leong and Lim had earlier claimed that they were unaware that Sgt Tan was a policeman. DPP Johannus disputed this by stating that Leong had seen the officer's police lanyard, which had been "conspicuously hung" around his neck.

The DPP added: "It is unbelievable that Lim would not have seen Sgt Tan's police lanyard... when Sgt Tan's body turned towards the direction of his group and was at that point, only an arm's length away from Lim."

Lim had also testified that his attack was prompted when Sgt Tan charged at him.

Goh had admitted that he knew Sgt Tan was a policeman who was on duty at the time. He, however, denied punching the officer.

The trio were each offered bail of $5,000 on Wednesday and will be sentenced on April 22.

For assaulting a police officer, offenders can be jailed for up to seven years and fined or caned. Leong cannot be caned as she is a woman.