A Brooklyn teen is in critical condition after hitting his head while surfing on an F train yesterday, police said.

Police were told by a motorman that the 17-year-old man was found unconscious and bleeding from the head while lying atop the last car of a southbound F train. He was injured while the train traveled between the Fourth Avenue and Smith-9th Street stations around 2:20 a.m.

This is the second subway surfer to get injured during the ride, following the death of a 45-year-old homeless man last Wednesday. The man was surfing on top of a southbound No. 6 train around 12:45 p.m. when he hit his head on a steel post, causing him to fall between the train cars near the 96th Street station. He died after being taken to Metropolitan Hospital.