Keeping the grandkids busy is my goal.  This tether ball is simple to assemble.  The bottom holds either water or sand.  We used water and this keeps the base completely stable.  The metal piping is easy to assemble.  The piping is a little loose and will sway a bit but we put a bar of cement down the center of the pole and this will stabilize it and make it a more sturdy hold.  The ball is made of a soft material to keep from hurting the kids hands.