Trespass occurs when a person enters property without permission or refuses to leave after permission is withdrawn and a person responsible for the property makes a clear request to the person to leave.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.