These are either on KPC or KickMax - you lunge forward in a deep lunge, while you do a hammer motion with your hand in a fist. Kind of like you are doing a VERY serious hammer of something right near your front foot. It's all one fluid motion - as you lunge down, you are hammering down. Then you push off the front foot to come back to standing. The lunges are LOW, and you are constantly moving, so it's a great endurance workout for the butt.
m.