When army regular Shawnald Lee Hong Heng found a man in his bedroom with his wife, he presumed he was taking advantage of her and punched him in the face repeatedly.

In fact, Mr Donovan Quek Hon Yong had taken her home after she got drunk during a night out with friends. For his efforts, the 25-year-old suffered fractures to the area around his right eye socket as well as loose and chipped teeth.

Yesterday Lee, 25, a military expert in the SAF, was jailed for five weeks after admitting hurting Mr Quek in his Yishun flat.

Deputy Public Prosecutor Jason Chua said that Mr Quek took Lee's wife, Ms Wong Kai Yan, 23, back to the flat in a taxi on July 10 last year.

Lee arrived with a friend soon after at 1.30am, planning to go out drinking if his wife was asleep. But when he saw his wife lying on the bed looking drowsy and Mr Quek sitting beside her, he punched Mr Quek. He stopped only when his wife intervened.

Lee then went downstairs but returned to the flat later and when he saw Mr Quek still there, he tried to hit him again - only to be restrained by his friend.

Mr Quek sought treatment after making a police report. He was given four days' medical leave and needed dental implants for two broken teeth.

Lee's lawyer, Mr T.M. Sinnadurai, asked the court to consider probation. He said his client, who has been with the army for five years, found his wife in her underwear and lost his self-control. He said Lee is taking care of their young daughter as his wife is now in a drug rehabilitation centre.

DPP Chua said Lee only told police that his wife was not wearing a shirt as she had vomited and taken it off. He asked for a sentence of six to 10 weeks' jail.

Lee could have been jailed for up to two years and/or fined up to $5,000 for causing hurt.