A viral video shows a frustrated passenger known as 'Viking Guy' taking out an unruly drunk shirtless thug with a sleeper choke on the subway.

Adrian Kaczmarek decides he has had enough when a 25-year-old man starts to harass riders at night on an Expo line in Los Angeles.

Other passengers fend him off, one with his bike, as the troublesome man stumbles around the train swearing and walking up to confront people.

Choke-down: A frustrated passenger known as 'Viking Guy' takes out an unruly drunk shirtless man with a sleeper choke on the subway

Drunk and disorderly: Other passengers have to fend him off, one with his bike, on an Expo line in Los Angeles

Confrontational: The troublesome man stumbles around the train swearing and walking up to confront people

Then in a swift and effective move Adrian, or 'Viking Guy', swoops in behind the man with a headlock and chokes him to unconsciousness on the floor of the train, before standing calmly on top of him.

Other travellers express their delight as Adrian keeps his foot on the man's chest, repeating the phrase 'stay down'.

He is unable to move from under the man's foot on the train travelling from the Crenshaw area to the Culver City Station around 9pm on Saturday.

Transit bosses late confirmed the man had been drinking and was under the influence of a controlled substance.

He was arrested for being drunk and disorderly.

Kaczmarek said: 'I was more concerned about my safety and the people on the train safety. I wasn't sure if he had a knife or if he had a gun.

Grip of a Viking: Then in a swift and effective move Adrian Kaczmarek swoops in and chokes the man to unconsciousness

Swift and smooth: He releases the man, who passes out, on the floor of the subway under the seats

Going nowhere: Other travellers express their delight as Adrian keeps his foot on the man's chest, repeating the phrase 'stay down'

'I finally saw it escalating to the point where he was getting physical and people are getting pushed around. The whole thing is about to explode. I thought the best thing to do was go over there and subdue him,' he told NBC Los Angeles.

The video of the incident was uploaded to YouTube over the weekend and has gone viral with over 1 million views.

Commentators have expressed their satisfaction with the smooth way the troublemaker is dealt with.

One wrote: 'That guys foot was like Thor's hammer. Can't be moved lol.'