To push to the limit, go all out, full speed.
A very colorful phrase, one needs to be careful when using "balls to the
wall". Although its real origin is very benign, mos
people assume it is a reference to testicles.
In fact it is from fighter planes. The "balls" are knobs atop the plane'
s throttle control. Pushing the throttle all the way forward, to the wall of the cockpit, is to apply full throttle.