Rule #1: Be at the right place at the right time.
That's exactly what we did in this case, completely by accident. My friends and I were just bumming around a random piazza in Florence when this man came around trying to hawk some tickets to us. By this point, we were quite wary of anyone who approached unsolicited, because most such approaches were just attempts to exploit "foolish tourists" who can easily be convinced to buy anything.
Maybe it was the extreme temperatures (heat wave of Summer '03), or just tiredness from walking around, but we decided to hear him out. After some attempts at explanation, he recognized quickly that no one in our party was fluent in Italian, so he resorted to charades. We could pick out the word "calcio", which is Italian for soccer (or "football" for you European readers). And after mimicking some soccer-ball handling, he would then go into this Mike Tyson's punch-out impression. Very strange, we thought, but maybe worth checking out for 20 euros/person.
So we filed into the makeshift arena that had just been assembled in Piaza di Santa Croce and took our seats in the "Blue" bleachers. The opposite side was the "White" section. As you probably guessed, these corresponded to the colors of the teams that competed that day.
Calcio Storico, it turns out, is a sporting competition that has been a Florentine tradition since the 16th century. Each quadrant of the city (Red, Green, Blue, and White) is represented by a team of 27 men. There are three matches total, one per week. The first two events are semi-final matches, and the winners of those two matches face off to determine the overall winner during the third week.
During each match, you see both teams line up in the center of an arena that is about two-thirds the length and width of a soccer field. A team scores by throwing the wooden ball between two horizontal lines on the opposite team's wall. But you realize quickly that the ball is hardly important in this game. As soon as the whistle blows, you see a massive fist fight erupt in the center of the arena. All 28 members of both teams are punching, kicking, and wrestling each other to the ground. When a player becomes incapacitated, they are removed from the field on a stretcher, and ambulances sirens are heard leaving the arena every 10 minutes or so. It's easily the craziest event we attended during our 21 days in Europe.
Calcio Storico is scheduled to take place annually around the time of the St. John's Day (patron saint of Florence) in late June/early July. See the official webpage (Italian only) at http://www.globeit.it/caf/.