National Guards and Sokol volunteers protested in Zagreb, leading to an armed clash with regiments of the Home Guard and former Common Army.

The Sokol movement is an all-age gymnastics organization founded in Prague in the Czech lands of Austria-Hungary in 1862 by Miroslav Tyrš and Jindřich Fügner. It was based upon the principle of "a strong mind in a sound body". Sokol, through lectures, discussions, and group outings, provided what Tyrš viewed as physical, moral, and intellectual training for the nation. This training extended to men of all ages and classes, and eventually to women.

On 5 December 1918, four days after the proclamation of the Kingdom of Serbs, Croats and Slovenes, the National Guards and Sokol volunteers suppressed a protest and engaged in an armed clash against the soldiers of the 25th Regiment of the Royal Croatian Home Guard and the 53rd Regiment of the former Austro-Hungarian Common Army. National Guardsmen stopped the soldiers at the Ban Jelačić Square in Zagreb.

The Royal Croatian Home Guard was the Croatian-Slavonian army section of the Royal Hungarian Landwehr, which existed from 1868 to 1918. The force was created by decree of the Croatian Parliament on December 5, 1868, as a result of the Croatian–Hungarian Settlement.

The Common Army, as it was officially designated by the Imperial and Royal Military Administration, was the largest part of the Austro-Hungarian land forces from 1867 to 1914, the other two elements being the Imperial-Royal Landwehr and the Royal Hungarian Honvéd. However, it was simply known as the Army (Heer) by the Emperor and in peacetime laws, and, after 1918, colloquially called the k.u.k. Armee.