They added that the incident happened between Sandhurst Road and Masjid stations around 6.05pm on Friday.
A S Bartakke, Senior Police Inspector of Wadala Railway Police Station told PTI that Mankhurd-resident Rudal Basu Nishad, a crane operator with a private construction company, died before he could be admitted to a hospital.
He added that a person named Kishore Ramrao Jawale (32)was nabbed by co-passengers and was handed over to the police.
A police official said that eye-witnesses have claimed that Nishad had a heated argument with Jawale in the train as it approached Sandhurst Road Station.
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Commuters then caught Jawale and handed him over to the Railway Protection Force which turned him over to the CSMT railway police.
However some eye-witnesses, the police official said, have also claimed that Jawale tried to snatch the victim's phone and the latter lost his balance and fell off the train. The phone fell inside the compartment, the official said.
Meanwhile inspector Bartakke said that the exact reason for the scuffle is yet to be ascertained.
"But we suspect that Jawale is mentally unstable," he said.