Country Dictionary

This refers to the governor on a steam engine. Two heavy balls are attached to the engine so that as engine speed increases, the centrifigal force of the flywheel causes the balls to rise. As the balls top out, they govern (limit) the engine, thereby controlling maximum engine speed. "Balls out," then, refers to running the engine at maximum speed.

The engineer was running the train at a "balls out" pace while trying to make up time.

Originally referred to the governor on old steam engines that had two ball that rotated across one another that would control speed depending on how fast they spun. Balls out meant going full speed or power.

That old steam tractor was going balls out.

giving your all in a certain situation, being courageous

You should've seen me out there, I started to choke but then I went totally balls out.

Old timey terminology: on steam engines, they had steel balls in there that resricted steam flow. When the conductor was ready to pick up speed, he'd yell "Balls out!", signaling the help to do just that, thereby letting them haul some ass.

"Balls out! We got to mow down those hobos!"

When things get really tough or crazy, and one has to try harder to accomplish a goal.

Holy shit, the football team scored a point under a minute on the 4th quarter! The other team has no other choice but to go balls out, dude!

In rugby when the other team sees the ball has left the scrump

"balls out," go tackle him

(adj) describing an extreme effort, supposedly dangerous. Analagous to "sticking one's neck out," but with a more important (allegedly) piece of anatomy

Man, Brian drove balls out around that corner, I thought I was gonna die.