45limpdick (MikeW) had the nerve to tell me I was wrong when I said "legally you can only defend yourself and your property." Sorry, I am correct.
The general common law principle regarding self-defence is stated in Beckford v R (1988) 1 AC 130:
"A defendant is entitled to use reasonable force to protect himself, others for whom he is responsible and his property. It must be reasonable."
The further one moves away from oneself, the less one can claim a right of self-defence. That would seem obvious since the right is "self-defence" not a "right to defend others". Of course, someone like 45limpdick (MikeW)gets his information from the Internet and doesn't check it with a lawyer to make sure it's accurate.
The right to defense of others turns largely on the reasonableness of the belief that the victim deserved assistance. A minority of jurisdictions require that the rescuer be a member of the victim’s family, or the victim’s superior or employee. Similarly, a minority of jurisdictions require that the rescuer’s belief be correct, reasoning that the rescuer ‘merely steps into the victim’s shoes’, while the majority requires only that it be reasonable. Pennsylvania law imposes no such restrictions. It does, however, require the additional showing that the rescuer believed that his intervention was necessary, and that the rescuer retreats if the victim would be required to do so.
If in the course of intentionally defending himself or another, a defendant recklessly or negligently injures or kills a third person, self-defense will not bar liability, but it will reduce the gravity of the charge from an intentional crime to a reckless or negligent crime.
Therefore, the further one removes oneself from the connection to the victim, the more tenuous the claim of a right to defend that person.