Wiktionary
balls-out
a. (context US idiomatic slang English) extreme, extremely great adv. 1 (context US idiomatic slang English) With great abandon. 2 (context US idiomatic slang English) At the fastest possible speed.
Usage examples of "balls-out".
It was late Saturday night, as I recall, when we learned that Frank Oliver had officially won the tournament -- by one fish, ahead of the balls-out poor-boy crew on Lucky Striker.