Early on the morning of 21 November, the IRA assassinated a group of British spies in Dublin. The GAA (Gaelic Athletic Association) who the British believed had ties to the IRA had a match of Gaelic Football on the same day in Dublin. The British believed that the IRA members would be in attendance of the Dublin VS Tipperary match and the soldiers were ordered to surround Croke Park and search the crowd.

The game had been underway for about 10 minutes when Croke Park was stormed by trucks filled with Royal Irish Constabulary, Auxiliary Police and Military men. However, for unknown reasons, shots were fired by police as soon as they reached the southwest gate at the Royal Canal end of Croke Park, at 3:25 pm. The police later claimed they had been shot at by "IRA sentries" but there was no evidence to suggest so with multiple witnesses saying otherwise. Best case scenario they mistook the ticket sellers standing outside as the so-called "IRA sentries".

The police kept shooting for about ninety seconds. Their commander, Major Mills, later admitted that his men were "excited and out of hand". Some police fired into the fleeing crowd from the pitch, while others, outside the grounds, opened fire from the Canal Bridge at spectators who climbed over the Canal Wall trying to escape. As the spectators streamed out, an armoured car on St James Avenue fired its machine guns over the heads of the crowd, trying to halt them.

The police had fired 228 rounds of rifle and revolver ammunition, while fifty rounds were fired from the armoured car outside the Park. Seven people had been shot to death, and five more had been shot and wounded so badly that they later died; another two people had died in the crowd crush. The dead included Jane Boyle, who had gone to the match with her fiancé and was due to be married five days later. Two boys aged ten and eleven were shot dead. Micheal Hogan was the only player to be killed but Jim Egan also was injured. A stand in Croke Park was later named after him.

The oldest was Patrick O’Dowd who was shot dead as he helped people over the wall, on what is now the Cusack Stand side of the ground. The youngest victim Jerome O’Leary (10) was shot through the head as he watched the match while sitting on a wall behind the Canal End goal. William Robinson (11) had climbed a tree at the corner of the Canal End on Jones’s Road from where he watched the match. A bullet entered his chest and exited through his right shoulder, after which he fell to the ground. Ticket seller Thomas Doyle ran to William's aid with the youngster begging of him: "Take me to mother." The police raiding party suffered no casualties.

A later press release would claim:

"A number of men came to Dublin on Saturday under the guise of asking to attend a football match between Tipperary and Dublin. But their real intention was to take part in the series of murderous outrages which took place in Dublin that morning. Learning on Saturday that a number of these gunmen were present in Croke Park, the Crown forces went to raid the field. It was the original intention that an officer would go to the centre of the field and speaking from a megaphone, invite the assassins to come forward. But on their approach, armed pickets gave warning. Shots were fired to warn the wanted men, who caused a stampede and escaped in the confusion."

The Times, which during the war was a pro-Unionist publication, ridiculed Dublin Castle's version of events, as did a British Labour Party delegation visiting Ireland at the time. British Brigadier Frank Percy Crozier, overall commander of the Auxiliary Division, later resigned over what he believed was the official condoning of the unjustified actions of the Auxiliaries in Croke Park. One of his officers told him that, "Black and Tans fired into the crowd without any provocation whatsoever". Major Mills stated, "I did not see any need for any firing at all".

Later that night, two high-ranking IRA officers, Dick McKee and Peadar Clancy, together with another man, Conor Clune, were killed while being held, interrogated and tortured in Dublin Castle.

Rember their names:

Jane Boyle (26),
James Burke (44),
Daniel Carroll (31), (died 23 November)
Michael Feery (40),
Michael 'Mick' Hogan (24),
Tom Hogan (19), (died 26 November)
James Matthews (38),
Patrick O’Dowd (57),
Jerome O’Leary (10),
William Robinson (11), (died 23 November)
Tom Ryan (27),
John William Scott (14),
James Teehan (26),
Joe Traynor (21),

Conor Clune (27),
Dick McKee (27),
Peadar Clancy (32),