For two reasons I guess. First, the area of contact, the hand palm is wide and it distributes the impact force of the hit. The second one is that the materials involved (if I can express myself like...
That depends upon the severity of the injury. At the minimum, the referee should call a foul. If there is a serious injury involved then it becomes a criminal offense which the police can...
You can see an attorney. The attorney will ask for a lot more details than you've given us and will be able to answer you. It may be possible to sue someone, but it may not; we really cannot tell...