jump the gun

Unperturbed when an overanxious opponent jumped the gun in the women's 60-yd. dash, willowy Wilma Rudolph exploded perfectly from the starting blocks.

Taking advantage of advance press releases, gabby Walter Winchell jumped the gun a full two weeks by announcing in his radio period and tabloid column that the 1933-34 prizewinner was Men in White by Sidney Kingsley.