In 1920 , following Westminster 's prominent announcements that it had the Irish insurgents on the run , Collins and his Squad killed several British secret service agents in a series of coordinated raids . In retaliation , members of the Royal Irish Constabulary went to Croke Park , where a G.A.A. football match was taking place between Dublin and Tipperary . The police officers opened fire on the crowd , killing twelve and wounding sixty . This event became known as Bloody Sunday . A stampede of panicking British operatives sought the shelter of Dublin Castle next day . About the same time , Tom Barry 's 3rd Cork Brigade took no prisoners in a bitter battle with British forces at Kilmichael . In many regions , the RIC and other crown forces became all but confined to the strongest barracks in the larger towns as rural areas came increasingly under rebel control
Bloody Sunday
Bloody Sunday (1920)
Michael Collins (Irish leader)