> You have not considered the phrase 'balls to the wall' before
> LINK · Wiktionary definition for 'balls to the wall'
...but you thought it was something testicular, right?
First attested in the 1960s in the context of aviation, in reference to ball-shaped grips on an aircraft's engine controls (typically throttle, prop pitch and fuel mixture). Pushing these "balls to the wall" would put the aircraft at maximum thrust. Analogous to pedal to the metal.