He was watching two police officers detain a female suspect when one of them shouted at him to move away.
He punched the officer in the face and got arrested as well.
Yesterday, Tay Hock Choon, 51, was jailed for three months for voluntarily causing hurt to the public servant.
Court papers said Tay was having drinks at V Restaurant in Lorong 13 Geylang at about 8.40pm on Oct 5 last year.
Criminal Investigation Department officer Muhammad Azzar Samsuddin, 28, and his partner were carrying out anti-vice enforcement duties in the area. They spotted a female suspect seated at the back alley of the restaurant. She fled into the restaurant when she saw them approaching and the officers gave chase.
Inside the restaurant, they identified themselves as police officers and managed to restrain her.
The struggle drew a crowd of onlookers, including Tay, who had gathered to watch, but ended up blocking the front entrance of the restaurant.
Mr Azzar, who was trying to lead the suspect out of the restaurant, once again identified himself as a police officer before ordering the onlookers to move away.
Tay punched Mr Azzar in the face and was arrested. Mr Azzar later sought treatment at Changi General Hospital for facial injuries. He was given a day's medical leave.
Yesterday, Tay pleaded guilty to one count of voluntarily causing hurt to a police officer in the execution of his duty.
Deputy Public Prosecutor (DPP) Kelly Ho said Tay had attacked a vulnerable part of the officer and that it was not his first violent crime.
Tay had been jailed 42 months and given six strokes of the cane for voluntarily causing hurt with dangerous means, among other offences, in 2008.
Tay, who was not represented by a lawyer, asked for leniency. He could have been jailed up to seven years, caned and fined.
This article was first published on May 18, 2016. Get The New Paper for more stories.