It is believed the tradition dates back to 1945, but opinions differ about how it began. As one story goes, there was an argument among some young men. They suddenly grabbed tomatoes from a street market and pitched them at one another, while other people cheered them on. A year later, they did it again, and a tradition was born. The authorities tried to stop it, but it was very popular, and in 1959 the Tomatina became an official event.
Does "an official event" refer to "a formal important thing" or something eslse? Thanks.
It turned into something accepted, recognised and on the calendar for the town.