Sharon, who created, owns and runs femaledom.com is a real ballbusting enthusiast. Her love of kicking men in their balls has made this site one of the best.
She has stated that although she loves to kick men in their balls, her favorite contact is kneeing a man in his balls. She says this is because she can deliver a much more forceful impact to his balls causing him more pain.
I liken it to this...if you want to kick a ball a long ways, you use your foot, because you get much greater velocity. If you want to brake a tree limb, you use your knee. Both deliver a lot of thrust.
I had the weirdest dream that some sexy girl had me on my back in my underwear with my legs open about to give me the knee. She kept teasing me and just before I go it I woke up.
I agree, the closeness is very erotic. The best is when my gf puts me against the wall and strokes my penis while kneeing me. I end up grabbing her butt pretty hard during impacts. What a fun game, it's hard to hold out long though.
Here's a very recent photo they put up showing two beautiful girls, Amy and Elaine, kneeing a naked guy in his balls. Wonderful expressions on the one girl's face as she watches!