Bloody Sunday was an event which took place in London, England on 13 November 1887, when a crowd of marchers protesting about unemployment and the Irish Coercion Acts, as well as demanding the release of MP William O'Brien, clashed with the Metropolitan Police. The demonstration was organised by the Social Democratic Federation and the Irish National League. Violent clashes took place between the police and demonstrators, many "armed with iron bars, knives, pokers and gas pipes". A contemporary report noted that 400 were arrested and 75 persons were badly injured, including many police, two policemen being stabbed and one protester bayonetted.

William O'Brien was an Irish nationalist, journalist, agrarian agitator, social revolutionary, politician, party leader, newspaper publisher, author and Member of Parliament (MP) in the House of Commons of the United Kingdom of Great Britain and Ireland. He was particularly associated with the campaigns for land reform in Ireland during the late 19th and early 20th centuries as well as his conciliatory approach to attaining Irish Home Rule.