If you are unfamiliar, the Tomatina Festival is a giant tomato food fight held every year in Brunol, Spain.
In 1944, during a parade of gigantes y cabezudos, young men who wanted to participate in the event staged a brawl. Since there was a vegetable stand nearby, they picked up tomatoes and used them as weapons. The police had to intervene to break up the fight, and forced those responsible to pay the damages incurred.
The following year the young people repeated the fight, only this time they brought their own tomatoes from home. They were again dispersed by the police. After repeating this in subsequent years, the party was, albeit unofficially, established.
Check out another awesome image of the fight after the break.