Yo-yoing wouldn’t be much without Physics.
If you know the Phsysics behind a trick, post it here!
When you dismount from a trapeze, the yo-yo will continue in a circular direction because of the forces acting on it. the yo-yo wants to continue in a horizontal direction, but the string is pull it inwards. This cause a diagonal resultant force. See the first picture below.
When you pull your hands together, it rids of the string’s force allowing for the yo-yo to travel in a straight direction. See second picture.