A district judge fined a businessman instead of jailing him for a bruising fight with a man alleged to be having an affair with his wife.

The prosecution, which is appealing against the sentence, had urged that Tommy Koh Leng Theng, 36, be jailed for at least three weeks for his "relentless" blows that continued even after Mr Ho Wei Siong, 42, was on the ground.

"But there were factors that mitigated against the seriousness of Mr Koh's actions", including his "emotional response to seeing Mr Ho, who he perceived was responsible for the breakdown of his marriage", said District Judge Adam Nakhoda.

Mr Ho was also "insolent" when asked if he had had an affair with Koh's wife, responding: "What if I have, what can you do?" This led to Koh overreacting, he added in judgment grounds released last week.

Koh had pleaded guilty to disturbing the peace when he fought with Mr Ho at Lorong 27A, Geylang on June 11, 2014.

Koh also agreed to an additional charge being taken into account during sentencing, which involved fighting with another man who had made advances on his wife in 2012.

The district judge agreed with Deputy Public Prosecutor Sarah Shi that since Koh had previously resorted to fighting to settle differences, he had to be specifically deterred from doing so in future.

In pressing for a jail term, DPP Shi pointed to the serious injuries Mr Ho suffered, among other things, saying he had bruises, abrasions and stitches on his left eyelid.

Lawyer Anil Singh, in defending Koh, argued that the incident was not premeditated, with Koh emotionally unstable because of his marriage breaking down.

He added that Mr Ho had used a plastic chair to hit Koh when the latter tried to punch him, after which the fight began.

Mr Ho, who was given six days' medical leave, had been issued a stern warning by the police for his part, noted the judge.

The district judge acknowledged the aggravating factors but ruled the "threshold" to merit a jail term had not been crossed, given the facts and circumstances of the case.

"I considered that imposing the maximum fine of $5,000 would be sufficient to meet the needs of specific deterrence," he said.