Lol
I've been grabbed by the balls before while doing martial arts NOT COOL! Quite painfull, lol. But you end up leaving yourself open by grabbing them to all kinds of other crap. Mainly you leave your face open, and in the end a face is more important than your balls. (Not that I would want to lose either)...
I guess it depends on who your fighting, if the're just being jerks than a nice strike to the balls will get them to back off, but if they want to hurt you it won't really do anything...

I've been grabbed by the balls before while doing martial arts NOT COOL! Quite painfull, lol. But you end up leaving yourself open by grabbing them to all kinds of other crap. Mainly you leave your face open, and in the end a face is more important than your balls. (Not that I would want to lose either)...
I guess it depends on who your fighting, if the're just being jerks than a nice strike to the balls will get them to back off, but if they want to hurt you it won't really do anything...