You don’t need to be a master of prestidigitation to figure this one out. All that is required is the power of observation or a little logic: You have observed that if you throw a tennis ball against a wall, it will stop and return to you. Simple. But how would you throw the same ball so it would completely stop, reverse itself and return to you even though it has hit nothing and is connected to nothing?
REVEAL THE ANSWER
You throw it up.