You may know the term “balls out” or “balls to the walls.” And you may have assumed that it has something to do with a certain part of the male anatomy. It makes sense. Another common term is “ballsy” meaning “courageous.” And it does refer to testicles – as if large testicles equate courage. Yeah sure.
“Balls out” can be used as an adjective or an adverb. As an adjective, it means “wild” or “extreme.” For example, “that was one balls-out street race!” As an adverb, it means “head-long” or “giving it one’s all.” As in “ we have to go balls out to win this game.”
However, the phrase has nothing to do with testicles and everything to do with steam engines. In the early days of these machines, Watt style engines used a centrifugal governor to control speed. The faster the engine went, the higher the balls on the centrifugal governor would rise. Going full speed was known as running “balls out.”