1. balls-out - Adjective
2. balls-out - Adverb
The metal balls of a centrifugal governor are pushed apart to a degree depending on the speed of a rotating shaft, providing negative feedback to the throttle
balls-out (not comparable)
(US, idiomatic, slang) Extreme, extremely great.
Descriptive of the use of a centrifugal governor at maximum speed, corresponding to full throttle.
(US, idiomatic, slang) With great abandon.
(US, idiomatic, slang) At the fastest possible speed.
Source: en.wiktionary.org