Cox v. Louisiana (1965)
In 1961 Elton Cox led students on a civil rights demonstration through the streets of Baton Rouge to the courthouse.  They kept to the side of the road so traffic would not be obstructed.  At lunchtime, Cox called for demonstrators to try to get service at one of the segregated lunch counters in the vicinity.  At this point, police fired tear gas at the crowd and arrested Cox.  He was convicted of disturbing the peace.  The US Supreme Court struck down the state law under which he was convicted, saying it was overbroad and not fairly applied.  The court said other parades and street meetings that blocked the street had been permitted under the law, and Cox had been deprived of the right of free speech and assembly.  The Court added that "the rights of free speech and assembly do not mean that everyone may address a group in any public place at any time."

http://www.oyez.org/cases/1960-1969/1964/1964_49/