turn tail

(idiomatic) To turn away from someone or something, in preparation for running away; to reverse direction; to leave or flee.

Example: 1838, Charles Dickens, "Some Particulars Concerning A Lion" in Mudfog and Other Sketches:
  A box-lobby lion or a Regent-street animal . . . will never bite, and, if you offer to attack him manfully, will fairly turn tail and sneak off.
1886, Robert Louis Stevenson, Kidnapped, ch. 21:
  [H]e stormed at me all through the lessons in a very violent manner of scolding . . . . I was often tempted to turn tail, but held my ground for all that.
1911, Jack London, The Cruise of the Snark, ch. 15:
  At last, in despair, we turned tail, ran out to sea, and sailed clear round Bassakanna.
1945 April 3, Bruce Rae, "Okinawa: The Marines Have Landed," New York Times, p. 1:
  Five of the enemy planes were shot down and the remainder turned tail.
2011 April 27, Vivienne Walt, "Have Fuel, Will Fight," Time:
  The men blew up two oil pipelines in eastern Libya near the rebel-held Sarir fields, before turning tail and speeding back west.