Biggest military upset ever?

[lfromnj]

Myeongnyang by Yi Sun Sin has to be up there.

[lfromnj]

I'm only thinking 20th Century here, but The Battle of Warsaw (1920) has to be up there. It wasn't called "the Miracle on the Vistula" for nothing.

Definitely a crucial moment for history as a whole but it seems both sides had somewhat equal manpower and the Poles basically had no supply line length while the Russians were at the end of their supply line.  IIRC there was a cavalry battle a week after this battle that was very lopsided and was one of the last calvary battles in history.

Edit: https://en.wikipedia.org/wiki/Battle_of_Komar%C3%B3w

Here we go. This was the last battle where it says people were still using calvary not just to move around. I assume this means they were actually shooting from their horses. The Poles were outnumbered 10:1 and inflicted insane casualties on the Soviets.

[lfromnj]

Another battle I would say is the Battle off Samar. One factor a lot of the other battles have in a list like this is that the winning side usually had a plan before the battle and may even have set a trap to win this. The most famous example would be say Cannae by Hannibal. However Samar was unusual in that the Japanese actually managed to lay a decent trap on paper and lured away the escort carriers so effectively this battle was a well planned ambush by the Japanese. Yet by some miracle the Americans managed to beat a far superior fleet forcing them to retreat.

The Americans only had a few destroyers and escort carriers which were slower and smaller aircraft carriers meant to really be behind a fleet. The Japanese had 4 battleships ,6 cruisers, and 11 destroyers.