The juicy battle in Ivrea is part of the town's yearly carnival, which recreates a centuries-old revolt by commoners against the monarchy.
The three-day carnival kicked off on Sunday and ends the day before Ash Wednesday, the first day of Lent in the Christian calendar.
"It's madness ... really madness," local resident Francesca told AFP. "Some may think these people are crazy, but for us in Ivrea, this is something we have in our DNA. Children are born with this madness."
According to the battle's official website, the orange fight has existed in one form or another since 1858. Huge crowds flock to the event annually, though the legend behind the actual insurrection is a bit murky.
As the most commonly told story would have it, a 12th century miller's daughter fought back against an evil baron when he came to her on the eve of her wedding to exercise his "jus primae noctis" - a reference to medieval lords having the supposed right to have sexual relations with subordinate women.
Instead, the bride cut off the baron's head and paraded it all over town, sparking the uprising.
Today, that revolt is recreated with townspeople in medieval attire battling teams of the tyrant's guards in period dress, complete with protective helmets and masks.
The townspeople, on foot and without any protection, throw oranges at the guards, who fight back from carts drawn by masked horses.
Crates of oranges are tightly stacked one over the other stand on the sidewalks, and some spectators take refuge to avoid being hit by wayward pulp.
Wearing a red floppy hat marks you as a spectator and safe from flying fruit.
"It is a historical reconstruction of a real fact which happened several hundreds years ago with the revolt against a king," said Roberto, who participated in the battle. "In the last century, the battle is waged with oranges but before we were throwing stones, if you can imagine that."