jump the gun

verb3

1. •
   To begin a race too soon, before the starting gun goes off.

   • Unperturbed when an overanxious opponent jumped the gun in the women's 60-yd. dash, willowy Wilma Rudolph exploded perfectly from the starting blocks. — 1961
2. •
   To act or begin too soon or without due caution.

   • The former prime minister appears to be jumping the gun, pre-empting the legal process that is just beginning to dig deeper. — 2006
3. •
   To trade securities based on information that is not yet public; to trade on inside information.