Possible defences to assault charges
What do I have to show in order to claim self-defence?
You’ll have a good defence to an assault charge if you were defending yourself or someone else. However, the amount of force you use has to be reasonable, given what you believed the situation to be.
So even if you were mistaken about the situation – for example, about whether the other person was going to attack you – you may still be able to claim self-defence. What’s important is whether it was an honest belief, not whether your belief was objectively correct.
But if your belief was mistaken, the force you used must still be reasonable when measured against your mistaken view of the situation.
Cases: (1989) 4 CRNZ 674 (CA); (2003) 20 CRNZ 319 (CA)
You don’t have to be reacting to an attack that’s already taken place – you can use force to prevent an attack that has been threatened and you believe is about to happen. In other words, you can use pre-emptive force.
Just because you’re angry or wanting revenge at the time, this doesn’t necessarily mean you aren’t acting out of fear of a potential assault, and therefore you may still be able to claim self-defence.
What does “reasonable” force mean when arguing self-defence?
What is reasonable depends on how immediate and how serious the force or threat against you was, and what chance you had to protect yourself without using force yourself – for example by backing away from the threat.
Cases: (2003) 20 CRNZ 319 (CA);  AC 814 (PC)
But although the force you use has to be reasonable in the situation as you saw it, this doesn’t mean it has to be in reasonable balance with the force or threat as you saw it. For example, you may not have had a choice about the means of defending yourself, and you may have used a knife that was at hand against someone who didn’t have a weapon. The courts have said that if you did what you honestly and instinctively thought was necessary to defend yourself from an attack, that would be strong evidence that what you did was “reasonable”.
Do I have to prove I was acting in self-defence?
Case:  1 NZLR 760 (CA)
No. It’s not up to you to prove you were acting in self-defence. All you have to do is point to some evidence on which a self-defence claim could be based; once you do that, the prosecution then has to prove beyond a reasonable doubt that you weren’t acting in self-defence. If you don’t raise the issue, then the prosecution doesn’t have to address the question.
In other words, you just have to raise the question, based on some real evidence – it’s then the prosecution’s job to exclude the defence.
Defending your home or possessions
Using force to defend your home
You’re justified in using reasonable force to prevent a person trespassing on your property, or to remove them.
However, you’re not allowed to hit or otherwise “strike” the other person, or cause them “bodily harm”. Pushing, shoving, fending off or obstructing the other person is allowed, so long as it’s proportionate and reasonable. Injuries to the other person like minor bruising will be acceptable, but any harm to them that’s more than “merely transitory and trifling” isn’t acceptable.
You’re also justified in using “necessary” force to prevent someone breaking into your home, if you believe on reasonable and probable grounds that the other person doesn’t have any legal justification for breaking in.
Using force to defend your possessions
You’re justified in using reasonable force to defend your possessions – this applies to any “movable thing”. “Movable” means what it says – it covers anything other than land and buildings, so it can include anything from your watch to your car.
This defence covers you if you do it under a “claim of right” – which means if you genuinely believe you have a legal right to the property. You can use this defence even if you’re mistaken about having a legal right to the property. It also doesn’t matter if it’s unreasonable for you to have this mistaken belief.
To put up a “claim of right” defence, you only have to point to some evidence that raises this as a possible defence. It’s then the prosecution’s job to prove beyond a reasonable doubt that you didn’t have a genuine belief. It’s not your responsibility to prove that you had this belief.
To use this defence, you’re not allowed to have hit or otherwise “struck” the other person, or caused them “bodily harm”. Pushing, shoving, fending off or obstructing the other person is allowed, so long as it’s proportionate and reasonable.