When and why do the Czechs celebrate Butchers' Day?

Taking a stand for quality meat

Butchers have always been butchers at heart, conscientious about the respectability and development of their craft. History proves that they have always stood on the side of justice, ready to defend it at any cost.
In 1310 Bohemia was ruled by King Henry of Carinthia, whose political incompetence led the country into misery and confusion. The Czech nobility therefore sided with Princess Eliška Přemyslovna, for whom John of Luxembourg was chosen as a husband.
When he arrived at the walls of Prague's Old Town on 28 November with the intention of attacking the city, it was the butchers who helped him defend himself against the Carinthian mercenaries. They fought them off from the St. Francis Gate, hacking through the city gate with butchers' axes and allowing John to enter Prague.
For this, the king gave the butchers a high award. They were allowed to wear the symbol of a white lion without a crown with one tail on their red banner or shield, and also use a seal of the same kind. The Master Butcher, who was at the head of the fight, was even appointed Mayor of Prague by John of Luxembourg.
Rescue of the Butcher's Church
The butchers that day also saved the Church of St. James, which has since been called "the Butcher's", from a marauding mob. The Prague butchers had many similar honourable deeds to their credit, and the king granted them unprecedented privileges and rights in return.
St. James is still regarded as the patron saint of the craft, and a mural depicting fighting butchers is still visible in the church. They may also have had a crypt built there for their services. Above its entrance is a Latin inscription which ends with the words 'Let not the butchers cut you', for theft in the church was punishable by having one's hand cut off.