How do you spot a back half on the trampoline?

Answer 1

Assuming you mean back handspring by back half...

Basically the same as if you're on the ground. Kneel behind the person and put one hand near their lower back (you can use two, but one should be fine). Guide them as they jump back. Basically just place your hand under their back and make sure they don't land on their head - push them over in the end if they need a little help getting over.

Of course, your spotting will depend on how well the person can do a back handspring already. If they need a lot of help with their back handspring and you're not really sure what you're doing - DO NOT SPOT THEM. They will most likely get hurt without a proper spotter, which it sounds like you're not.