From:
http://tkdtutor.com/07Defense/Laws.htm
Defense of property
Generally, where only property is involved and the offender makes no threat against a person, the use of force is not justified. If a person approaches you and demands your wallet, but makes no threats whatsoever, you may refuse the request, but you may not use force against the person. Remember there must be the threat of force and/or an overt action of force. In general, the law does not view property as important enough to justify the use of force to protect or regain it. An exception to this general rule is "hot pursuit."
Hot pursuit
If you witness the theft of your property and make a "hot pursuit" to recover it, you may use minimal force to recover the property but you may not cause serious injury. If the thief responds with force, you may use a reasonable amount of force to defend yourself, but you must end the confrontation as soon as possible. If your pursuit is not immediate or you did not see the actual theft, then the "hot pursuit" justification no longer applies.
Defense of home
To the law, your home is your castle. It is your place of last retreat. You are not required to retreat from a threat in your home. When defending your home against a burglary, authorities rarely question the use of force¾ even deadly force. Burglary is legally defined as:
the breaking and entering,
without consent,
of the dwelling house of another,
while it is occupied,
at night,
with the intent to commit any felony or larceny therein.
If you believe a burglar is serious physical threat to you or your family, the law allows you to use whatever force you feel is necessary to neutralize the threat. However, here again, one must be careful since not all intruders are burglars. Someone may be intoxicated and enter the wrong apartment. A firefighter may be trying to break-in to warn you of a fire in your home. Wildly shooting at anyone who trespasses onto your property is not reasonable self-defense. If the mistaken use force is reasonable under the circumstance and no one is seriously injured. the law will generally excuse the action. However, remember that the victim may still pursue you in civil court.
The use of force is justifiable only if the actor first requests the intruder to desist from his interference with the property, unless the actor reasonably believes that:
Such request would be useless,
It would be dangerous to the actor or another person to make the request, or
Substantial harm will be done to the physical condition of the property which is sought to be protected before the request can effectively be made.
The use of deadly force is not justifiable in the defense of premises unless the actor reasonably believes that:
The person against whom the force is used is attempting to dispossess the actor of his/her dwelling otherwise than under a claim of right to its possession; or
The person against whom the force is used is attempting to commit or consummate arson, burglary, robbery or other criminal theft or property destruction; except that
Deadly force does not become justifiable under A or B unless:
The person against whom it is used has used or threatened deadly force against, or in the presence of, the actor or
The use of force other than deadly force to prevent the commission or consummation of the crime would expose the actor, or another in his/her presence, to substantial danger of serious bodily harm.
These are defenses to criminal charges which will be brought against you if you defended yourself. Even if the prosecutor or police decide not to bring criminal charges against you or if you are successful in proving that you were protecting yourself as permitted under certain provisions of the criminal code, the attacker if injured still may attempt to bring a civil suit to recover for any medical expenses or injuries incurred.
Trespassing
Trespass occurs when a person enters property without permission or refuses to leave after permission is withdrawn and a person responsible for the property makes a clear request to the person to leave. If the person does not leave, he/she is considered a trespasser. As such, you may use minimal force to eject the trespasser, but you may not cause serious injury. The proper response to a trespasser is to notify the police. However, if the trespasser enters your property in a violent manner, you need not request him/her to leave before using reasonable force to eject the trespasser.
The use of force upon or toward the another person is justifiable when the actor is in possession or control of the premises or is licensed or privileged to be thereon and he/she reasonably believes such force is necessary to prevent or terminate what he/she reasonably believes to be the commission or attempted commission of a criminal trespass by such other person in or upon such premises. A person commits a criminal trespass if, knowing that he/she is not licensed or privileged to do so, enters or surreptitiously remains in any structure or separately secured or occupied portion thereof.
Do not assume every trespasser is a burglar. A problem arises when a trespasser is on your property and you believe the trespasser may try to break and enter your home, but he/she has not yet attempted to do so. You cannot legally treat the trespasser as a burglar until he/she at least attempts to break and enter. On the other hand, if you treat the person as a simple trespasser, you may place yourself or your family in more danger than if you threat the person as a burglar. This is a judgment call that hopefully you will never face. If this situation does occur, the law will likely excuse your use of greater force than necessary if, in fact, the trespasser was planning to commit burglary. Such things as the person wearing a mask or carrying burglary tools may help prove this. However, if the intruder was merely a simple trespasser, authorities may prosecute you if you used excessive force.
Some have stated that, if you kill a trespasser make sure he/she is inside the home, even if you have to drag him/her inside after the shooting. This action would in itself be a crime, even if it were later determined that the initial shooting was justifiable.
One is not permitted to set up traps to kill or maim persons who attempt to trespass on his/her property. There is a responsibility to warn trespassers of dangerous conditions and an inherent risk of injuries. You may not use a deep pit to catch trespassers or rigged shotgun to kill a trespasser.