throw in the sponge informal
throw in the towel informal

Three weeks after I started, the poor man who tried to lead us threw in the towel.

After 32 e6, Black could have thrown in the towel.

Or do you want to throw in the towel now?

All I know is, you've got to act like it has, or you might as well throw in the towel.

There were many times I wanted to throw in the towel.

Two weeks ago I was ready to throw in the towel.

Maybe I should say they didn't throw in the towel.

But now she was ready to throw in the towel.

"I saw a fight last almost two hours before one guy threw in the towel."

Some guys just never knew when to throw in the towel.