A stranger sucker-punched a woman — and broke her nose — because she tried to stop him from bothering other female straphangers inside a Brooklyn subway station, cops said

The 52-year-old victim was on the No. 2/5 platform inside the Church Avenue station in East Flatbush shortly before 7:15 p.m. March 21 when she spotted the stranger allegedly harassing women and tried to intervene, police said.

He followed her to the street level, where footage released Wednesday night shows the man waiting at the top of the stairs for her.

The video shows him walk up the stairs before the woman and turn around to face her.

“Now I can hit you,” he told her, according to a police source.

As she ascends to the street level and tries to pass him, the brute sucker-punches his victim in the face, the footage shows.

The victim was treated at the scene for a broken nose, but was not immediately taken to the hospital.

Cops are still looking for her attacker, who is described as approximately 20 to 30 years old with shoulder-length braids.