The Hard Hat Riot occurred on May 8, 1970 in Lower Manhattan. . The riot started about noon when about 200 construction workers mobilized by the New York State AFL-CIO attacked about 1,000 high school and college students and others protesting the Kent State shootings, the American invasion of Cambodia and the Vietnam War near the intersection of Wall Street and Broad Street. The riot, which spread to New York City Hall, lasted little more than two hours. More than 70 people were injured, including four policemen. Six people were arrested.

http://en.wikipedia.org/wiki/Hard_Hat_Riot