OverhandThe momentum will decrease a bit when you freeze your arm (prior to the switch).
When the arm stops, the nunchuk will continue rotating but since it isnt getting any new momentum from your hand it will decay.
Once you catch it you give it a quick boost again.
Without knowing what is hard I can still try giving some pointers:
Try to swing the nunchuk a wee bit upwards to counter the drop that happens when you let go of the stick.
Let go of the stick later than you are now. I just know for myself that sometimes I let go of the stick too early it will lessen the momentum more than if I do a late release. Make sure that the stick you are holding is pointing precisely forward (the way you are looking), meaning your knuckles will point towards your far-side.
Other than that, just give it time. There arent many chuckers out there doing this move at all, so it is pretty much undiscovered territory still
