It is well possible, that in "teach yourself self-defense in 2 hours" classes they may teach you to go after the balls.
But in my experience, in serious martial arts, they tell you not even to try going after the balls if in a serious self-defense situation:
1. Balls are naturally in a protected location and
2. It is much easier to inflict serious pain (and harm) in many other places of the body.
3. (This may be just for me) They may like it!