Excuse Me, Is It Here They Beat Up People?(1976)

Original title: Przepraszam, czy tu biją?

The film is a story of a young man coerced into undercover work for the police, in return for their dropping of charges against him. He is to befriend a leader of a gang of juvenile delinquents who plans big robbery of a jewelry store. The scheme works and the gang is caught in the act except the gang leader.