Under tort principles, a victim who accidentally injures a third-party in the course of defending himself is also protected from suit by that third party. A majority of jurisdictions also allow the defense of victims only if the victims themselves have a right to self-defense.
Thus, if the rescuer makes a mistake regarding the victim’s right to self-defense, he too will be liable. However, there is a strong modern trend toward protecting rescuers from suit if their wrongful assistance of a victim is based on a reasonable mistake (Pennsylvania tort law allows for a reasonable mistake). The rescuer may use as much force as the victim could have used in self-defense.
To remember is that whether or not you will be exonerated, you Will still need to retain an attorney to defend you, and that attorney will charge you $$$...
Now you need to answer who will pay for such defense?