I can think of one such battle in the British Isles; the battle of Bannockburn in 1314 in Scotland. In that battle, a 14,000-man English army despoiled a bunch of "homeless" vagrants on their way to meeting Robert Bruce. Bruce's 7,000 man army stopped the English army cold at Bannockburn creek with a downhill charge. Then between 1,000-2,000 vagrants formed an "army" and hit the English in the rear. It's not clear that they actually won the battle for Bruce, but it's clear that they were helpful to a Scots army outnumbered 2 to 1. Wiliam Wallace vs. Robert Bruce: Why Did One Win and One Lose?
1) For the purposes of this question, "Continental Europe" refers to anything outside of the British Isles, Australia, or the Americas (where "militias" were fairly common). Basically, anything on what I call the "Eur-As-Af" land mass. Feel free to use Asian or African examples.
2) "Peasants with pitchforks" refers to civilians that fought only in the one battle, using lethal but "non-standard" weapons. This rules out "government issue" weapons like swords, spears, bow-and-arrow, and guns, but allows pitchforks, hoes, scythes, clubs, knives, hammers and sickles, etc., basically anything that a civilian might pick up on the spur of the moment. "Battle" refers to an action of at least 1,000 men on both sides, with the "peasants" fighting regular soldiers armed with conventional weapons (for their time), not other "peasants with pitchforks."
3) "Decided" means that if the "peasants" were fighting on the same side as regular soldiers, these regulars were outnumbered (as Bruce's men were) or otherwise at a disadvantage against the enemy, meaning that a good argument can be made that the "peasants" provided the margin of victory.
Have "peasants with pitchforks" (a concept put forth by America's Pat Buchanan), in fact, "decided" battles under the above conditions? Put another way, how dangerous were such fighters?
Hints: I have a recollection of peasants winning battles for Poland's Thadeusz Kosciusko in 1794-5, but don't know if they were armed with "pitchforks" or conventionally. Ditto for the victors of the battle of Courtrai in 1302.