An alibi is used to show that the defendant could not have committed the crime because she or he was not at the scene of the crime when the offence was alleged to have been committed, but rather, was somewhere else.

This evidence may be given by the defendant and by other witnesses on the defendant's behalf.

Under s 124 of the Criminal Procedure Act 1921 (SA) if a defendant proposes to introduce evidence of alibi at the trial of an indictable offence in the Supreme Court or the District Court prior notice of the proposed evidence must be given, which is filed at the same time as the defence case statement is filed. This is not required if the essentially the same evidence was given at the preliminary examination where the defendant was committed to trial [s 124(3)].

In cases of assault and sexual assault it may be a defence that the person complaining of being assaulted gave consent (free and voluntary agreement ) to the alleged assault. For example, in many sports, where players anticipate and agree to a certain level of contact.

This is a particularly difficult area of the law - please see further descriptions of the law in this area in our sections on Rape and Indecent Assault.

There are some people who cannot legally consent, for example children (see in particular the handbook sections on child sexual assault, and unlawful sexual intercourse). Another example is where there is undue influence on people with a cognitive impairment (see further the handbook section on Sexual offences where the victim has a cognitive impairment (for example an intellectual disability).

Under s 15A of the Criminal Law Consolidation Act 1935 (SA) a person is entitled to use such conduct as he or she genuinely believes is necessary and reasonable to defend property from being taken, destroyed, damaged or interfered with; to prevent criminal trespass; to remove a trespasser; or to arrest someone unlawfully at large - as long as the conduct was reasonably proportionate to the threat the defendant genuinely believed to exist, and if the conduct resulted in death, the defendant did not act recklessly or intend to cause death.

However, see also: Home invasion where the requirement of reasonable proportionality does not apply.

It is a partial defence to a charge of murder (reducing the offence to manslaughter) in some circumstances [s 15A(2)].

Criminal trespass in relation to this defence is where someone comes on to a property with the intention of committing an offence (against the person or property) [s 15A(3)].

If a defendant raises this defence then it is for the prosecution to disprove it beyond reasonable doubt [s 15A(4)].

From 29 March 2021

If a defendant asserts that the offence occurred in circumstances of family violence, the questions of whether the defendant genuinely believed that particular conduct was necessary and reasonable to defend property, and whether that particular conduct was reasonable proportionate to the particular threat, are to be determined having regard to any evidence of family violence admitted during the course of trial. For the legislative definitions of circumstances of family violence, and evidence of family violence see sections 34V and 34W of the Evidence Act 1929 (SA) [Criminal Law Consolidation Act 1935 (SA) s 15B(2)-(3)].

Common law defence

A defendant may raise the defence of duress where the immediate threat of death or serious personal violence was so great that it overcame the defendant's resistance to carrying out the criminal act. There is a subjective and objective test involved in assessing this defence.

Duress cannot be a defence to murder [ R v Howe [1987] AC 653].

For offences allegedly committed on or after 1 February 2021

Statutory defence of duress

It is a defence to a charge of an offence (other than a prescribed offence*) if at the time of carrying out the conduct constituting the offence, the defendant reasonably believed that a threat had been made that would be carried out unless:

objectively, the conduct was a reasonable response to the threat.

However, the statutory defence of duress will not apply if such a threat was made by or on behalf of a person with whom the defendant was voluntarily associating for the purpose of carrying out conduct of the kind actually carried out.

The statutory defence of duress is not available for prescribed offences which include:

[see Criminal Law Consolidation Act 1935 (SA) s 15D]

From 29 March 2021

If a defendant asserts that the offence occurred in circumstances of family violence, the questions of whether the defendant reasonably believed that a particular threat would be carried out, or whether the defendant reasonably believed that particular conduct was the only reasonable way a particular threat could be avoided, or whether the particular conduct was objectively a reasonable response to a particular threat, are to be determined having regard to any evidence of family violence admitted during the course of trial. For the legislative definitions of circumstances of family violence, and evidence of family violence see sections 34V and 34W of the Evidence Act 1929 (SA)[Criminal Law Consolidation Act 1935 (SA) s 15B(2)-(3)].

From 1 February 2021, it is a defence to a charge (other than a prescribed offence*) if the defendant carried out the conduct constituting the offence in response to circumstances of sudden or extraordinary circumstance and at the time of carrying out the conduct:

1. the defendant reasonably believed that:

AND

2. objectively, the conduct was a reasonable response to the emergency.

An emergency need not involve a risk of death or serious harm.

If a defendant raises such a defence, the defence is taken to have been established unless the prosecution disproves the defence beyond a reasonable doubt.

The defence is not available for prescribed offences which include:

From 29 March 2021

If a defendant asserts that the offence occurred in circumstances of family violence, the questions of whether the defendant reasonably believed that particular conduct was the only reasonable way a particular threat could be avoided, or whether objectively the particular conduct was a reasonable response to a particular threat, are to be determined having regard to any evidence of family violence admitted during the course of the trial. For the legislative definitions of circumstances of family violence, and evidence of family violence see sections 34V and 34W of the Evidence Act 1929 (SA) [Criminal Law Consolidation Act 1935 (SA) s 15B(2)-(3)].

It is not generally a defence to criminal conduct that a defendant was intoxicated by alcohol or drugs at the time the offence was committed. However, Part 8 of the Criminal Law Consolidation Act 1935 (SA) [ss 267A - 269] allows an intoxication defence in limited circumstances.

The defence of intoxication recognises that alcohol and drugs can impair a defendant's ability to form the required mental intention to commit a criminal offence. A defendant may successfully raise a defence of intoxication if they can show that their intoxication impaired their consciousness to the point of criminal irresponsibility [s 268(1)].

Intoxication will not be available as a defence if the defendant formed an intention to commit the offence before becoming intoxicated, and became intoxicated to strengthen their resolve to commit the offence (colloquially known as "Dutch courage") [s 268(1)].

Intoxication is generally not a defence when the intoxication is self-induced [s 268(2)]. Recreational use of a drug is considered self-induced. Where intoxication arose from both recreational and therapeutic use of one or more drugs, the resulting intoxication is also considered self-induced.

A person found mentally incompetent to have committed an offence, in circumstances where the trial judge is satisfied that the mental incompetence was substantially caused by self-induced intoxication, will usually be dealt with under Part 8 rather than Part 8A [s 269C(2)] unless the judge orders otherwise in the interests of justice [s 269C(3)]. See Mental impairment.

Self-induced intoxication operates as a partial defence to certain offences that require a specific intent and foresight of the consequences of certain actions. A person who assaults another while impaired by self-induced intoxication may, if the person dies, be found guilty of manslaughter but may not be found guilty of murder [see s 268(3), (4)].

Intoxication is a complicated defence and should not be raised or relied upon without legal advice and representation.

Generally, every person is presumed to be mentally competent to commit a criminal offence [Criminal Law Consolidation Act 1935 (SA) s 269D].

A person charged with an offence may raise a defence of mental incompetence if, at the time of the alleged conduct, they were suffering from a mental impairment such that they:

[Criminal Law Consolidation Act 1935 (SA) s 269C(1)]

Mental impairment can include a mental illness, an intellectual disability or a disability or impairment of the mind resulting from senility [s 269A].

The defence of mental impairment recognises that the criminal law responds to and punishes physical conduct that occurs with a criminal intent or guilty mind. A person who commits an offence but who was not aware of their conduct or did not understand that it was wrong ought not be held criminally responsible and liable to criminal sanction. See also Elements of a Criminal Offence.

A defendant who raises mental impairment as a defence to alleged conduct must prove it on the balance of probabilities.

A defendant, their lawyer or the prosecution must inform the court as soon as possible if they have reason to believe that the defendant may have been mentally incompetent to commit the charged offending [Joint Criminal Rules 2022 (SA) r 67.2]. The defendant's lawyer (if they have one) must also inquire into the defendant's mental competence as soon as possible if concerns are raised.

Where the defence of mental impairment is raised, the question of the defendant's mental competence must be separated from the remainder of the trial [s 269E(1)]. The trial judge may choose to start with the objective (physical) elements of the offence or the mental competence of the defendant [s 269E(2)].

A defendant found to have committed the objective elements of an offence but who successfully relies on a defence of mental impairment will have a finding recorded of "conduct proved but not criminally responsible due to mental incompetence". Prior to 14 July 2025, such a defendant would be found "not guilty by reason of mental impairment". This terminology changed on 14 July 2025 to better reflect the defendant's level of responsibility in the conduct.

A person found mentally incompetent to have committed an offence, in circumstances where the trial judge is satisfied, on the balance of probabilities, that the mental impairment was substantially caused by self-induced intoxication, may be dealt with under Part 8 of the Criminal Law Consolidation Act 1935 (SA) rather than Part 8A [s 269C(2), see Intoxication]. Intoxication will be regarded as self-induced if it results from the recreational use of a drug or the combined effect of the therapeutic consumption of a drug and the recreational use of a drug [s 269A(2a), (2b)]. The court may nevertheless order that a defendant whose mental impairment was substantially caused by self-induced intoxication be dealt with as mental impairment under Part 8A, having regard to the circumstances of the intoxication and the interests of justice [s 269C(3)].

A person found to have committed the objective elements of an offence but who was mentally incompetent at the time of the offending may be released unconditionally, released on licence for a specified period or detained in secure psychiatric care [ss 269NB and 269O]. It is a condition of every licence that the defendant be prohibited from possessing firearms and ammunition. The court may also direct a defendant to surrender a firearm [ss 269NC and 269OA]. When determining whether to release a defendant, either unconditionally or on a licence, the paramount consideration must be the safety of the community [ss 269NA and 269NI].

Supervision orders are governed by Chapter 2 Part 2 of the Uniform Special Statutory Rules 2022 (SA).

Provocation is not a defence to a charge of assault. It can only be used as a defence to reduce a charge from murder to manslaughter (it is not a complete defence). In any other case it cannot be used as a defence although, after conviction, it can be taken into account by the court when considering an appropriate penalty.

The provocation defence is only available where the defendant hears first hand of the thing that provokes them.

This is where a person in the defendant's situation, and who has the defendant's characteristics, but possessed of ordinary self control, would be so affected by the victim's words and actions as to lose self-control as the defendant did.

The provocation has to have actually caused the loss of self-control and act as the defendant did, and it is not merely an act of vengence.

The gravity of the provocation has to be assessed by reference to the relevant characteristics of the accused and then the question is whether the provocation of that gravity would have caused the ordinary person to lose self-control (viewed objectively and without the characteristics of the accused except maturity and age) [See : R v Lindsay (2014) 119 SASR 320].

A person is entitled to use such conduct as he or she genuinely believes is reasonable and necessary for a 'defensive purpose' (that is, in self-defence or in defence of another, or to prevent or end an unlawful imprisonment) under s 15 Criminal Law Consolidation Act 1935 (SA).

If a defendant raises a defence under this section, the defence is taken to have been established unless the prosecution disproves the defence beyond reasonable doubt.

This will be a complete defence to an offence, including murder, as long as the force used was, in the circumstances as the defendant genuinely believed them to be, reasonably proportionate to the threat the defendant genuinely believed to exist (for example, see Zecevic v DPP (1987) 162 CLR 645). See however the exception to reasonable proportionality in: Home invasion.

It will be a partial defence to murder, reducing the offence to manslaughter, if, despite the defendant believing his or her actions were necessary, the conduct was not reasonably proportionate to the threat that the defendant believed existed.

From 29 March 2021

If a defendant asserts that the offence occurred in circumstances of family violence, the questions of whether the defendant genuinely believed that particular conduct was necessary and reasonable for a defensive purpose, and whether that particular conduct was reasonable proportionate to a particular threat, are to be determined having regard to any evidence of family violence admitted during the course of trial. For the legislative definitions of circumstances of family violence, and evidence of family violence see sections 34V and 34W of the Evidence Act 1929 (SA)[Criminal Law Consolidation Act 1935 (SA) s 15B(2)-(3)].