Tort Law - Trespass
Trespass to the Person - Defences
Defence of Others
The law of self defence extends to defending not only oneself, but any other person, and is specifically applicable to the work of a security guard or body guard. It is lawful to intervene to the hurt or injury of an attacker who is attacking someone else. The same rule apply as in self defence – the threat must be credible or the danger real, what is done to repel the attack must be reasonable, and any other viable option short of counter-attack must be tried first.
Public Necessity, Private Necessity and Prevention of Suicide
who have acted in breach of a law for purposes of readily apparent emergency. However authority on it is not entirely certain and it is seldom used. Necessities can include preventing suicide or serious harm to or from a third party. It would not include any reason that would be seen as trivial or capricious. A good case on this is In Re F which dealt with a psychiatric patient who was sterilised to prevent unplanned pregnancies, but not in a fit state of mind to give or withhold consent. To lunge at and tackle a person unexpectedly would ordinarily be considered battery. But if done to clear the person from the path of an oncoming motor vehicle, it is considered a necessity. Whereas you would normally need consent – express or implied – there is no need where a readily apparent necessity arises.
The two main differences between this defence and the defence of others defence are firstly, that here the would-be plaintiff is not attacking anyone else. Secondly, it covers damage done to property for preventative purposes, not just in responding to an offence already in action. This defence operates where a defendant is compelled, or feels compelled, to act contrary to the law, but only if the need is clear.
In Re F (Mental Patient: Sterilisation)  2 AC 1.
Is Provocation a Defence?
As it stands, where an attacker is provoked by the victim, the sum claimable in exemplary damages (for particularly bad behaviour by the plaintiff) is reduced proportionally to the degree of provocation. Commonsense dictates that provocation should be a complete defence to trespass to the person, so that compensatory damages can be reduced also, and even, a claim defeated altogether in circumstances of sufficient severity. Everyone knows that to attack or threaten another person is a lesser moral offence, if it was in response to a seriously provocative act on the part of the victim. The law, however, sees this differently. In Fontin v Katapodis, it was ruled by the High Court that provocation is not available as a defence for the assailant. This ruling has held sway across the common law world and courts have continually expressed a high-minded attitude toward the use of violence. In short, DO NOT use physical contact as a solution to provocative (yet non-violent) behaviour or else you, your employer and/or your client, will be liable to an award of damages. The only other alternative is that you, yourself, will be criminally liable. (See the chapter on criminal law).
Importantly, because Fontin was a ruling of the High Court, no other court in Australia can overrule it. The author is of a view, however, that this law can and should be overruled by the High Court, but it would take a very serious case indeed and a very strong argument to warrant going to the High Court to have a law from a prior decision overruled. The argument revolves partly around the basis on which Fontin and other similar cases have been decided, as well as contributory negligence, and policy arguments related to well known principles of human behaviour.
The application of this in civilian law enforcement is the same as that of false imprisonment, above. If faced with a confrontation, a person might be attacked, threatened or prevented from leaving if the other party is of poor character. The enforcement activity may present a lot of people with provocation, but they cannot rely upon that to mitigate their culpability. The same applies if a person acting in an enforcement role reacts badly in the same situation. Where the resulting harm is overwhelmingly serious and the quantum of damages warrants action at the High Court, an argument may lie to alter this law.
 In Re F (Mental Patient: Sterilisation)  2 AC 1.
 Fontin v Katapodis (1962) 108 CLR 177.
 Pingree, Andrew, Provocation as a Complete Defence to Trespass to the Person (2010) 15:2 DLU 205.