Here's a lil explanation to ya'll on how to do jackhammers. I think this is also a variation of a handglide...but harder.... In this move you hop on you're hand in da handglide position so the hand the supports you're whole weight actually comes off da ground. So you jump around in circles.

1) First try then spinning motion. Get in da handglide position and by using only you're left hand (which is in yo stomach) try to turn a lil' bit. Sort of turn you're hand from you're wrist so you are clearly turning. Do this back & forth. After that you should try hoppin'.
2) So once again you are in da handglide position. Now by using you're legs and you're free hand for help try to jumping in this position. This move is called The Cricket.
3) Once you've got that down cold then try jackhammers. Now you put you're free hand behind you're back or something. You don't use it for any kind off help. So you're one hand does everything: Hopping, balancing and turning. You're legs shouldn't touch da ground at all.

It's possible to f*ck up you're knees while doin' diz one 'coz they are GOING to hit the ground when you practice this. This move is NOT easy...And NOT for beginners. You can hurt you wrist pretty seriously if you can't hold da handglide position. You should pretty much master the position!! Keep practicing & Keep it real!!!