Although the cause of the riots is disputed, repeated demands by the police and army personnel that the marchers relinquish their flags reportedly became a flashpoint.

A call for reserves brought several mounted police who charged their horses directly into the crowd and swung their clubs indiscriminately.

[1] In this ensuing melee, over twenty marchers were severely injured by the clubs, and ambulances from nearby hospitals were dispatched to rescue the many wounded.

[1] Later in the evening, Ruthenberg's socialist party headquarters on Prospect Avenue was ransacked by soldiers, police, and armed civilians.

"[1] Towards the end of the day, the anti-socialists piled "scores of red flags and banners" — which they had taken by force from the marchers — at the foot of the Soldiers and Sailors' Monument in Public Square and set them alight in a giant bonfire.

[4] This account is disputed by the IWW in the newspaper The New Solidarity, in which they outline that those there, celebrating May Day had not violated any city ordinance to incite rioting, and that the then Republican mayor of Cleveland, Harry L. Davis, had issued an order to the police to suppress any violations of law with "promptness and firmness" setting the tone of how police should respond to the event.