@Yongmei0
I think you should ask yourself the same questions your insurer would ask :
- was the basketball hoop self-standing or fixed to the ground?
- did your guest picked the parking spot by himself or you have told him to park exactly there?
- Is it possible to turn over the basketball hoop with a ball or someone had to jump on it / hung himself on it?
.... these sort of questions. As far as I know, the responsibility depends if this accident happened because of guest's rough negligence or because the hoop was not fixed properly.