Police tell Eyewitness News they're investigating whether he had been surfing on a train.
They say it's possible a fixed object struck him.
The incident held up service for several hours. 7 and N trains ran on alternate tracks and were delayed.
The victim's identity has not yet been released.
"Surfing" subway trains, meaning lying on top, is illegal, and authorities consider it a common but dangerous activity that often involves youthful daredevils.
(The Associated Press contributed to this report.)
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