turn one's coat

• turn coat

From the practice of turning one's uniform coat inside out in order to hide the colors reflecting one's allegiance.

turn one's coat

1. (idiomatic) To turn against a previous affiliation or allegiance.
   • 1819, Sir Walter Scott, A Legend Of Montrose:

     To meet the exigence of the moment, a considerable army was raised under General Baillie, a Presbyterian officer of skill and fidelity, with whom was joined in command the celebrated Sir John Urrie, a soldier of fortune like Dalgetty, who had already changed sides twice during the Civil War, and was destined to turn his coat a third time before it was ended.

   • 2012, Nigel Tranter, The Wallace, →ISBN:

     Bruce would scarcely have found this sufficient cause to turn his coat.

   • 2014, Scott Stanley, Betrayal of the Cloak, →ISBN, page 44:

     He also knew that here, in Connecticut, the chance of finding rebels who would turn their coats was far greater than it was in Boston which, for over two years now, had been the epicenter of the unrest that threatened peace with Britain.

2. Used other than with a figurative or idiomatic meaning: see turn,‎ coat.

• change sides, defect

• turncoat