"Balls to the wall" has nothing to do with anatomy (nor does balls-out). https://en.wiktionary.org/wiki/balls-to-the-wall#English https://en.wiktionary.org/wiki

"Balls to the wall" has nothing to do with anatomy (nor does balls-out). https://en.wiktionary.org/wiki/balls-to-the-wall#English https://en.wiktionary.org/wiki/balls-to-the-wall#English https://en.wiktionary.org/wiki/balls-out#English https://en.wiktionary.org/wiki/balls-out#English