Medieval Italians were full of beans, and they worked them out partly through intense intramural rivalries. Florence, notably, was torn apart in Dante's day by the Guelph and Ghibbeline factions that forced the poet into exile. The Venetians managed to stay clear of that tiff, preferring to duke it out on the rather safer terms of geography: east siders versus west siders.
The inhabitants of the western sestieri were called the ‘Nicolotti’ after their headquaters, the ancient church of San Nicolo dei Mendicoli, where they elected their ‘Doge dei Nicolotti’, who would lead them in all their races, regattas, games and general punch-ups (battagliole) against the other half of the population in the east, known as the ‘Castellani’ after the sestieri of Castello.
Like modern gangs, one could identify them by their colours: the Nicolotti wore black caps and scarves; the Castellani wore red. The Venetians were famous for their boxing skills, and any worker or tradesman with a powerful punch could work his way up to 'doge'.
Even foreigners were given a faction, depending on where they first set foot in Venice (the train station was considered Nicolotti territory; the cruise ship port definitely is).
Their respective patches overlapped at San Trovaso, which was considered neutral territory, and given identical facades and entrances (one for each side). Still, if things degenerated, they could all troop over for a brawl on the nearby Ponte dei Pugni.
Images by: Fondazione Musei Civici Venezia