No one can argue that nuts are sensitive, but they're rarely time sensitive.
Have you thought about trying to pleasure this opponent with your mouth, rather than whatever you were going to do to him that would make the sturdiness of his nuts relevant? Lick, don't punch! A person will have a hard time opposing you if your mouth is full of their junk.
I guess this might be an after school fight or a test of manhood at the local Y, so maybe a full on, balls-deep, drooly-chest blowjob isn't appropriate. In that case, attack the other most sensitive parts of a man's body. His eyes or his ego.
Short Answer: "How long has your hair been thinning?" + thumb in the eye.