How about: Battle of the Golden Spurs
An army of Flemmish peasants with nothing more than maces, improvised polearms(reworked pitch forks...), the Geldon and a few swords.
The Flemmish had about 9000 men, all infantry. (The 400 nobles never really did anything.) They had no armor, but a few self-made leather vests.
The French had 8000 men,but 2500 were noble cavalry, the rest consisted out of crossbowmen, spearmen and other infantry.
About a thousand cavalerists were killed and another thousand got wounded.
The French Royal army had to retreat, which was a disgrace for the King of France, to lose against the counts of Flanders.
Unfortunately, the Flemmish lost the following battles.