From Chimes at Midnight (Falstaff), by Orson Welles. Often discussed as the greatest battle sequence committed to film.
The visceral, rapid editing creates a fast, disorienting picture of hand-to-hand brutality. It's this sequence that inspired the opening to Martin Scorsese's Gangs of New York. Watch how closely Scorsese follows the rhythm of the Welles battle for the same effect.