A security camera was rolling when Brooklyn’s bully dean, whom an appellate court is forcing the Department of Education to rehire, clobbered a teen in the hallway, according to court papers.

It “was live action, like a television show or . . . a movie,” said IS 218’s former principal, Joseph Costa.

The dean, Peter Principe, had told The Post he was trying to defend a female teacher when the incident transpired, but the recording disproves his defense, according to court papers.

The tape, which clearly shows him attacking the student, did not convince the state Supreme Court’s Appellate Division to stand by the city’s decision to fire him.

On it, Principe “grabbed [the 13-year-old student] by the collar, slammed him into the wall, held onto [the student’s] collar as he walked past three classrooms and pushed him into [his] office,” the principal said.