white flag, show the - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Also, hang out or hoist the white flag. Surrender, yield, as in Our opponents held all the cards tonight, so we showed the white flag and left early. This expression alludes to the white flag indicating a surrender in battle, a custom apparently dating from Roman times and adopted as an international symbol of surrender or truce. [Late 1600s]