A teenager attacked the founder of the anti-crime group Guardian Angels in New York City last week, socking him in the face in an attack on the street, police said Tuesday.

The teenage thug allegedly hit Guardian Angels founder Curtis Sliwa, 64, with such force on the Manhattan street that his teeth were knocked out, the New York Post reported.

The activist and radio host told the police he had been walking up the stairs out of a subway station when he witnessed four teenagers fighting on Friday night.

Authorities say one of the teens followed Sliwa down West 33rd Street near Eighth Avenue before ambushing him from behind and striking him in the face.

The force of the blow caused Sliwa to lose his front left tooth, police said.

A spokesperson for the NYPD said it is unclear what the teen’s motive was for attacking him. Silwa declined medical attention at the scene and could not identify the alleged attacker.

The Guardian Angels, which Sliwa founded in 1979 when crime reached historic levels in New York City, patrol the city streets unarmed to report crimes as they happen. Members of the group typically wear red berets and jackets when they are on duty.

The organization also has hundreds of chapters throughout the world, including major cities like London and Los Angeles.