根据南澳的Criminal Law Consolidation Act 1935 (CLCA) 其中规定，法官需要考虑s15(3）规定的防卫对象，可以是自我防卫（self defence）,防卫别人（defence of another）, 结束非法拘禁（ prevention or termination of the unlawful imprisonment）. 在这个过程中，防卫的行为是否满足 s15(1)(a)
(a) that the respondent genuinely believed that the conduct to which the charge related was necessary and reasonable for a defensive purpose; and
- 嫌疑人真的认为自己的安全受到了威胁。that the respondent genuinely believed that the safety of his person was threatened and, if so,
- 嫌疑人真的认为自己需要采取行动来防卫。whether the respondent genuinely believed that he had to act to defend himself from that threat, and, if so,
- 嫌疑人真的认为自己的行动是合理和恰当的。whether the respondent genuinely believed that it was both necessary and reasonable to do so in the way he did in order to defend himself.
这里和学生签的GTE要求一样是一个主观的测试。嫌疑人当时的心理活动是需要评估的对象。而不是评估一个正常人在当时的情况下应该怎么做。“It is a subjective test in the sense that it is the belief of the accused which must be examined. The court is not, at this stage, concerned to examine whether a reasonable person would hold that belief.”
考虑嫌疑人的心理活动不仅需要考虑嫌疑人怎么说，还需要考虑嫌疑人所处的场景”The concept of a genuine belief carries with it the necessity to consider not only what the accused person may say as to his belief but whether, in all the circumstances, that stated belief was genuine”: see Gillman (1994) 62 SASR 460
根据Wells J in Morgan v Colman 考虑这个嫌疑人是否真的认为受到了威胁（the genuineness of the belief of an accused person ）的问题的指导性原则 如下
- (a) Defence means defence; a person who claims to have been acting in justifiable self-defence must have acted, and believed himself to have been acting, in defence. To engage willingly in combat is not acting in self-defence. 积极参与争斗不是正当防卫
- (b) Self-defence can never be made to cover for aggression; if a person provokes, or deliberately leads, another to attack him, and he then uses that attack as an excuse or pretext for attacking the other person, he cannot cry defence. 主动挑衅不是正当防卫
- (c) Self-defence can never be called in aid to justify retaliation or revenge if the danger is over, and the occasion for self-defence is at an end. 在危险过去后的报复行为不是正当防卫
- (d) A person who, according to the circumstances as he understands them, genuinely believes that he is threatened with an attack, is not obliged to wait until the attack begins. A person so threatened may use reasonable measures to make the situation safe, and he does not act unlawfully merely because he forestalls or tries to forestall the attack before it has begun.” 正当防卫不一定要在攻击发生之后，如果受到的威胁，可以先采取行动解除威胁。
- (b) the respondent’s conduct was, in the circumstances as the respondent genuinely believed them to be, reasonably proportionate to the threat that the respondent genuinely believed to exist.
15 （1）(b) 说的是一个适度性原先，嫌疑人的防卫在当时的情况下是否适度。简而言之需要客观的考虑，在嫌疑人主观认为的威胁下，他的反应是否适度。
“ In short, the test requires an objective assessment to be made of the reasonableness of the response of the accused having regard to the nature of the threat which the accused subjectively and genuinely believed to have existed.”
嫌疑人是否真的认为，在当时的情况下，他的防卫行为是恰当的 （having regard to the trails of the moment, whether he used reasonable force or he plainly overstepped the mark）
“If the prosecution failed to prove beyond reasonable doubt that either was not a reasonable possibility, it had failed to prove its case.” Police v Lloyd 1998
所以要想合理的用正当防卫的理由打室友。必须首先有一个合适的场景，在这个场景下，你主观上判断你受到了威胁。比如室友闯入你的房间， 你让他出去，他拒绝，你可以使用暴力把他推出去。 特别是考虑到 15C—Requirement of reasonable proportionality not to apply in case of an innocent defence against home invasion。 你可以对他狠一点。
“It is more than possible that the defendant genuinely believed that in order to safeguard himself from blows struck with the walking stick it was necessary and reasonable to physically push the elderly man away from the back of the truck. It is probable that he held this belief.
It is also probable that the defendant genuinely held the belief that if he tried to go about his business, in the process losing the use of his arms as a defensive shield, he would be struck with the walking stick.
On the evidence, the reasonable possibility has not been excluded that the defendant genuinely believed that the elderly man had deliberately swung the walking stick dangerously close to the defendant while the defendant was in the back of the truck, putting boxes on the ramp. Such a belief may have been without foundation, just as the elderly man’s belief that he had been endangered by the driving may well have been without any real factual foundation, but it is reasonably possible that it was held by the defendant.
If there was a genuine belief in those circumstances, I am of the view that the conduct was reasonably proportionate to the threat. It is reasonably possible. The defendant’s verbal attempts to end the discussion and go about his business had been unsuccessful. While a punch would clearly have been disproportionate, I am unable to say that attempting to shove the elderly man aside and out of reach, in order to be able to safely retrieve the boxes, was unreasonably disproportionate to the threat the defendant probably believed he faced.
The prosecution has not excluded the possibility that the defendant acted with a defensive purpose. It is reasonably open on the evidence.”