To do this nunchaku trick, you must move fast your hand from behind your body to the front, to catch again the nunchaku, if not it may hit you or may fall. Also try to move your torso a little back so the nunchaku have more room to spin in midair. It is “between the legs” and not “under the leg”, because both legs are in the ground when the nunchaku is passing under them, and in all the other aerials videos, when it was under the leg, the leg were the nunchaku was going under, wasn’t touching the ground.
Same hand catch slow motion:
Other hand catch slow motion: