To begin, let's start off with some "fun" facts about testicles. As you know they are part of the male reproductive organs that hang outside of the body, and although they are sensitive and covered in nerve endings they are actually pretty durable.
The average set of balls can take up to 60 psi before rupturing and breaking. They are also inherently protected by the fact they sit in a scrotum. This allows the balls to move around upon impact with out absorbing the full force of the hit.