Rail authorities say the incident took place on Wednesday at the Philippi Station on the Central Line.
The man was assaulted after he climbed through a window to get into a stampvol train.
Nobody tries to assist the bleeding man, who was then thrown off the train by an angry commuter.
Donna Venter, a trade union representative for the United National Transport Union (Untu) and who works for the Passenger Rail Agency South Africa (Prasa), says the drama unfolded when the man’s bag hit someone while he was climbing through a window.
Venter explains the carriage had been full at the time and that the male commuter became angry and stabbed the man in the bum.
“The other commuter was furious. There was no space to move on the train due to the overcrowding. The man got so angry that he stabbed the commuter in the left bottom buttocks and threw him out of the window again.”
She says the injured man managed to hang onto the open window with his hands until the train came to a stop at Nyanga Station.
The man was then helped by another commuter to climb back through the open window.
Steve Harris, the General Secretary of Untu, says overcrowding on trains has become problematic: “The overcrowding of the trains now is a direct result of the vandalism of train coaches by furious commuters who started torching coaches when trains were delayed due to cable theft or other infrastructure-related problems.”