throw in the towel

throw in the towel AND throw in the sponge (surrender, give up, admit defeat, stop fighting) — cдаться, признать поражение

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Boxing rules are now such that a referee must stop a fight if he thinks one of the contestants has taken enough punishment. In earlier and rougher days a boxer's second could call a similar halt by throwing into the ring the towel or sponge normally kept ready to hand to refresh his man between rounds.

see also
[show the white feather]