An element of the New York Police Department’s stop-and-frisk practice was deemed unconstitutional by a federal judge on Tuesday, a ruling that may have broad implications for the city’s widespread use of police stops as a crime-fighting tactic. The decision, the first federal ruling to find that the practice under the Bloomberg administration violates the Fourth Amendment protection against unreasonable search and seizure, focused on police stops conducted in front of several thousand private residential buildings in the Bronx enrolled in the Trespass Affidavit Program. Property managers in that program have asked the police to patrol their buildings and to arrest trespassers. . .