It happened on the Q line at the Seventh Avenue subway station in Park Slope just after 11 p.m. Tuesday.
According to police, this all stemmed from a verbal dispute among straphangers.
The victim was taken to New York-Presbyterian Brooklyn Methodist Hospital and is expected to recover.
Meanwhile, an active investigation is underway as police canvassed the train at the Seventh Avenue stop for any clues.
The violence comes as a shock to some who frequent the Brooklyn subway station..
"It's a complete surprise. I wouldn't expect it at this station. Sometimes in the back of my mind but now it's definitely a lot more present. I'm going to be thinking about my safety a lot more, a commuter told Eyewitness News.
According to the NYPD, subway crime dropped nearly 16 percent in November and more than 6 percent year-over-year.
Right now, police are looking for the attacker who got away at this station.
The person was last seen wearing a grey sweatshirt and black pants.
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