They Died with Their Boots On (All Region DVD) 1941 Errol Flynn, Olivia de Havilland, Arthur Kennedy

A highly fictionalized account of the life of George Armstrong Custer from his arrival at West Point in 1857 to his death at the battle of the Little Big Horn in 1876.
Director: Raoul Walsh
According to "The Guinness Book of Movie Facts and Feats", 3 men were killed during the cavalry charge scene. One, Stuntman Bill Mead's horse tripped while riding alongside Errol Flynn. As he was going down, he had the presence of mind to throw his sword forward to avoid it, but bad luck caused the hilt to get stuck in the ground and Mead fell on it, impaling himself.