Police say a 58-year-old man was stabbed in the shoulder and bitten on the head on a northbound L train at the Graham Avenue station in Williamsburg around 3 p.m.
They say a verbal dispute led to the attack.
The victim was taken to Bellevue Hospital in serious, but stable condition.
No arrests have been made, but police say they are looking for a man wearing all black and a ski mask.
L trains ran with delays in both directions for a short time.
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