According to The Straits Times, the victim, Joe DeMarini from Pennsylvania, uploaded the video on his Facebook page on Thursday.
The video showed an elderly man repeatedly using offensive language and assaulting a man on an MRT train.
DeMarini said the man was allegedly drunk and approached him and his friend and made sexual advances on him. When his female friend intervened, the man yelled and threatened her.
“He touched me, and I told him not to, and I briefly lost my temper – after that, he slapped me on the side of the head,” DeMarini was quoted saying by Singapore daily.
The 4-minute 22-second clip has gone viral on social media and has been viewed more than 1.2 million times.
The police said they received a report yesterday about a man who had repeatedly used offensive language and assaulted a commuter on an MRT train.
Police officers from Ang Mo Kio division identified the suspect and arrested him on Friday.
In Singapore, those convicted of the offence of public nuisance can be fined up to S$1,000 (RM3,148), while those convicted of the offence of voluntarily causing hurt can be jailed for up to two years or fined up to S$5,000 (RM15,744) or both.