This is something my
Sensei taught me when I studied
Jiu Jitsu. When someone tries to
kick you in the balls, it's very unlikely that it will be a horizontal kick connecting the ball of their foot with your
testicles. Also, it is highly unlikely that they will try to connect their toe with your testicles alone. The reason is that both of these require a level of precision that the average assailant simply will not have. What they will do is bring their foot up in an arc between your legs, attempting to contact your testicles, which are the lowest point of your crotch, with the top of the foot, the front of the ankle, or the lower shin. As you can imagine, this requires a very low degree of precision, it's almost impossible to miss.
The technique to counter this is deceptively simple. Stand with your feet approximately shoulder-width apart, with one foot slightly in front of the other, with the heel and toe level, and the front foot turned slightly inwards. Now thrust your hips forward and down. There should be almost no actual movement, but you will feel your buttocks pressed tightly together. This has the effect of making a pad of muscle from the upper-inner-back of your thighs the lowest point between your legs.
Now when someone kicks you, it will still hurt because after all you are still absorbing the force of the impact, but it is by no means enough to do you any real damage. I personally have used this technique to great effect. When somone kicks you in the balls, they fully expect you to go down - the idea you need to convey is that they did kick you, but that you are in total control of the pain. Pause for a second, grimace, then turn your leading foot straight and release the tension in your hips with a reverse punch straight to your opponent's upper chest.
Incidentally, Sensei also said that if you do want to kick someone between the legs, the objective is to follow through with enough force to at least knock them over, and if possible break the pelvis.
This wu provided for information purposes only!