What justifies a person using force against a trespasser?

The justification for using force against a trespasser primarily hinges on the concepts of possession of the property and the belief in immediate necessity. When a person possesses a property, they have a legal right to defend that property against unauthorized intrusions. If a trespasser enters the property without permission, the property owner may reasonably believe that it is necessary to use force to prevent further intrusion or to remove the trespasser, especially if there is an immediate threat to their safety or the safety of others.

Possession indicates not just physical control but also legal authority over the premises, which legitimizes the response to a trespass. Additionally, the belief in immediate necessity supports a quick reaction to protect one's rights and safety, which courts recognize as justifiable in circumstances where there is an immediate threat.

Other options, while they may seem relevant, do not capture the fundamental legal principle that justifies the use of force in these situations as effectively as the chosen answer does. For instance, the presence of a court order or legal representation is not always necessary or relevant in active situations, and witnessing an act of trespass, while important, does not equate to the legal justification provided by possession and the need for immediate response.