Squirrels are known to have a large testicle-to-body-ratio, i.e. they have lage lesticles in relation to the body. During mating season, male squirrels fight for females and territory. During such fights, the male squirrel tucks away his testicles into a furry pouch in order to protect them. Sometimes, however, a male is suprised by a rival and must fight quickly, leaving no time to tuck away the testicles. Consequently, the squirrel has to fight "balls out," a term that has come to refer to heated, all-out confrontations in the human world.
Wow, that squirrel there snuck up on the other one and made him fight balls out. Guess that settles that procreation conflict for the next few weeks.