An Australian businessman attending the Ultra Music Festival in 2016 pushed a police officer in plain clothes off a concrete block while the latter was sitting there and monitoring human traffic flow.

When told that he was disrupting police work, Wayne Liang asked to see the warrant card of Sergeant Alex Zhang Zhengyang. When the officer produced his card, Liang took a look at it, muttered "so what", and stamped on the officer's left foot.

A two-day special hearing was held in October last year to determine if Liang, 39, conducted himself in a loutish and aggressive manner, and had stamped on Sgt Zhang's foot in defiance of his authority.

Yesterday, District Judge Kessler Soh imposed a fine of $10,000 on Liang, who admitted to using criminal force on the 28-year-old officer.

Judge Soh said he did not find that Liang had acted defiantly in total disregard of authority. He accepted the defence's submission that his momentary defiance of authority was out of character and was probably a result of his intoxication.

"All in, I found that the defendant could not have behaved in a loutish and aggressive manner as submitted by the prosecution," he said.

The judge was also not persuaded that Liang's intoxication ought to be taken as an aggravating factor in the case. He said there was no credible evidence that Liang had acted in a rowdy manner and that his conduct had caused alarm to other members of the public.

Deputy Public Prosecutor Daphne Lim had told the court that Sgt Zhang, who was in plain clothes while on duty, was tasked to observe human traffic flow for crowd management at the Ultra Music Festival on Sept 10, 2016.

He was sitting on a concrete block and observing the situation at the junction of Bayfront Avenue when Liang pushed him off the block and took his seat.

When asked why he did that, Liang replied: "What?" Sgt Zhang repeated his question in Mandarin and Liang replied "I happy" in English.

Sgt Zhang identified himself as a police officer and told Liang he was disrupting his work. Liang asked for his warrant card. When Sgt Zhang produced it, Liang took a look at the card and the officer. He muttered "so what" and stamped on the officer's left foot. Liang was arrested.

After the sentencing, DPP Lim applied for a stay of execution on the fine and bail for Liang, pending the prosecution's appeal. She had asked for at least four weeks' jail.

But Judge Soh said he saw no reasonable basis to order it, and allowed Liang to pay his fine.

The maximum penalty for the offence is four years' jail and a fine.