There are several ways of going about this.
- If you make the tennis racket “independent”, it should not get warped with any other body movements.
- There is also a fairly new Magnet feature if you want to be able to let go of the racket (E.g. drop it). When turned on, the racket will be stuck to the hand, but you can turn the magnet off and it will drop to the ground (or go flying off etc).
- If you don’t want to do either of the above, put sticks down the length of the racket to stop it warping In the rigging panel (this is easiest approach, but does not guarantee zero warping).
I would also check the mesh - that image has lots of watermarks on it, so the mesh computation probably would not work well, so you will probably see strange mesh warping unless you clean up the image. Turn the yellow mesh icon on (bottom of scene/rig window) to see if the yellow mesh follows the shape of the puppet correctly.
To move the racket, I would put a dragger on the hand so you move the hand and the racket follows the hand.