throw in the towel

Example: “After three hours stuck on the puzzle, I threw in the towel.”

Origin: Boxing, but the towel is a replacement. The original idiom was "throw up the sponge," attested from the 1860s and referring to the sponge a second used to wipe down a fighter between rounds; tossing it into the ring was the corner's visible signal that their man was finished. As towels displaced sponges as standard corner equipment, the wording followed, and "throw in the towel" is documented from around the 1910s. What made either gesture necessary is worth noting: a beaten fighter often could not or would not concede for himself, so the authority to stop the fight rested with the corner, and the thrown towel was how they exercised it — a public admission of defeat made on behalf of someone in no condition to make it.