The one-hour food fight won’t start until a competitor climbs a greased pole to retrieve a ham, as the crowd hoots and cheers. Trucks bring in low-quality tomatoes from the province of Extremadura, and water cannons are fired to start the battle. (Participants are encouraged to squish the tomatoes to lessen their impact.)

Afterward, the cobble streets are hosed down, and the acidity of the tomatoes is said to leave them shining.

Karen Zraick contributed reporting.

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