Duck, You Sucker! (Italian: Giù la testa, lit. "Duck Your Head", "Get Down"), also known as A Fistful of Dynamite and Once Upon a Time ... the Revolution, is a 1971 epic Zapata Western film directed and co-written by Sergio Leone and starring Rod Steiger, James Coburn, and Romolo Valli.

Set during the Mexican Revolution of the 1910s, the film tells the story of Juan Miranda, an amoral Mexican outlaw, and John Mallory, a former member of the Irish Volunteer Army. After they accidentally meet under less-than-friendly circumstances, Juan and John involuntarily become heroes of the Revolution, despite being forced to make heavy sacrifices.

It is the second film of Leone's unofficial Once Upon a Time Trilogy, which includes the previous Once Upon a Time in the West (1968) and the subsequent Once Upon a Time in America (1984). The last western film directed by Leone, it is considered by some to be one of his most overlooked films.