A federal judge ruled Thursday that police can no longer use tear gas on protesters without declaring an illegal assembly, giving them fair warning and time to vacate the area. The temporary restraining order comes just weeks after the last rounds of heavy protest in Ferguson in response to a St. Louis County grand jury’s decision not to indict the police officer who shot and killed Michael Brown Jr. A group of protesters had filed the lawsuit asking for a restriction on police use of tear gas and excessive force during demonstrations.