1
general::
Also, throw in the towel. Give up, acknowledge defeat, as in I can't move this rock; I'm throwing in the sponge, or Bill decided to throw in the towel and resign from his job. This idiom comes from boxing, where formerly a fighter (or his second) conceded defeat by throwing the sponge or towel used to wipe his face into the ring. [c. 1900]
American Heritage Idioms
2
general::
Phrase(s): throw in the sponge
Go to throw in the towel and throw in the sponge; toss in the sponge
McGrawhill's American Idioms And Phrasal Verbs