When a person (usually a woman, but men can too) strikes a male's testicles with their foot, resulting in the kickee being immobilized by pain and possibly sterilizing or emmasculating him.
Wendy was tired of his cheating so she gave him a devastating kick in the balls
When someone has literal or figurative control of a man through a grip on his testicles (getting his conpliance by squeezing or threatening to squeeze them.
Mike was doing dishes because Ann had him by the balls (literal)
Big business has the world by the balls (figurative)