In criminal and civil law, assault is an attempt to initiate harmful or offensive contact with a person, or a threat to do so.  It is distinct from battery, which refers to the actual achievement of such contact.
An assault is carried out by a threat of bodily harm coupled with an apparent, present ability to cause the harm. It is both a crime and a tort and, therefore, may result in either criminal and/or civil liability. Generally, the common law definition is the same in criminal and tort law. There is, however, an additional criminal law category of assault consisting of an attempted but unsuccessful battery. The term is often confused with battery, which involves physical contact. The specific meaning of assault varies between countries, but can refer to an act that causes another to apprehend immediate and personal violence, or in the more limited sense of a threat of violence caused by an immediate show of force. Assault in many US jurisdictions and Scotland is defined more broadly still as any intentional physical contact with another person without their consent; but in England and Wales and in most other common law jurisdictions in the world, this is defined instead as battery. Some jurisdictions have incorporated the definition of civil assault into the definition of the crime making it a criminal assault intentionally to cause another person to apprehend a harmful or offensive contact.
Assault usually accompanies battery if the assailant both threatens to make unwanted contact and then carries through with this threat. See common assault. The elements of battery are (1) a volitional act (2) done for the purpose of causing a harmful or offensive contact with another person or under circumstances that make such contact substantially certain to occur and (3) which causes such contact. Thus throwing a rock at someone for the purpose of hitting him is a battery if the rock in fact strikes the person, and is an assault if the rock misses.
- cause serious bodily injury to another person with a deadly weapon
- have sexual relations with a person who is under the age of consent
- cause bodily harm by recklessly operating a motor vehicle during road rage; often referred to as either vehicular assault or aggravated assault with a motor vehicle.
Aggravated assault can also be charged in cases of attempted harm against police officers or other public servants.
Although the range and precise application of defenses varies between jurisdictions, the following represents a list of the defenses that may apply to all levels of assault:
Exceptions exist to cover unsolicited physical contact which amount to normal social behavior known as de minimis harm. Assault can also be considered in cases involving the spitting on, or unwanted exposure of bodily fluids to others.
Consent may be a complete or partial defense to assault. In some jurisdictions, most notably England, it is not a defense where the degree of injury is severe, as long as there is no legally recognized good reason for the assault.  This can have important consequences when dealing with issues such as consensual sadomasochistic sexual activity, the most notable case being the Operation Spanner case. Legally recognized good reasons for consent include surgery, activities within the rules of a game (mixed martial arts, wrestling, boxing, or contact sports), bodily adornment (R v Wilson  Crim LR 573), or horseplay (R v Jones  Crim LR 123). However, any activity outside the rules of the game is not legally recognized as a defense of consent. In Scottish law, consent is not a defense for assault. 
Arrest and other official acts
Police officers and court officials have a general power to use force for the purpose of performing an arrest or generally carrying out their official duties. Thus, a court officer taking possession of goods under a court order may use force if reasonably necessary.
In the United States, the United Kingdom, Australia and Canada, corporal punishment administered to children by their parent or legal guardian is not legally considered to be assault unless it is deemed to be excessive or unreasonable. What constitutes "reasonable" varies in both statutory law and case law. Unreasonable physical punishment may be charged as assault or under a separate statute for child abuse.
Many countries, including some US states, also permit the use of corporal punishment for children in school. In English law, s. 58 Children Act 2004 limits the availability of the lawful correction defense to common assault under s. 39 Criminal Justice Act 1988.
Prevention of crime
This may or may not involve self-defense in that, using a reasonable degree of force to prevent another from committing a crime could involve preventing an assault, but it could be preventing a crime not involving the use of personal violence.
Defense of property
Some jurisdictions allow force to be used in defense of property, to prevent damage either in its own right, or under one or both of the preceding classes of defense in that a threat or attempt to damage property might be considered a crime (in English law, under s5 Criminal Damage Act 1971 it may be argued that the defendant has a lawful excuse to damaging property during the defense and a defense under s3 Criminal Law Act 1967) subject to the need to deter vigilantes and excessive self-help. Furthermore, some jurisdictions, such as Ohio, allow residents in their homes to use force when ejecting an intruder. The resident merely needs to assert to the court that he felt threatened by the intruder's presence.
This defense is not universal: in New Zealand (for example) homeowners have been convicted of assault for attacking burglars.
Assault is an offence under s. 265 of the Canadian Criminal Code.  There is a wide range of the types of assault that can occur. Generally, an assault occurs when a person directly or indirectly applies force intentionally to another person without their consent. It can also occur when a person attempts to apply such force, or threatens to do so, without the consent of the other person. An injury need not occur for an assault to be committed, but the force used in the assault must be offensive in nature with an intention to apply force. It can be an assault to "tap", "pinch", "push", or direct another such minor action toward another, but an accidental application of force is not an assault.
The potential punishment for an assault in Canada varies depending on the manner in which the charge proceeds through the court system and the type of assault that is committed. The Criminal Code defines assault as a dual offence (indictable or summary offence). Police officers can arrest someone without a warrant for an assault if it is in the public's interest to do so notwithstanding S.495(2)(d) of the Code.  This public interest is usually satisfied by preventing a continuation or repetition of the offence on the same victim.
Some variations on the ordinary crime of assault include:
- Assault: The offence is defined by section 265 of the Code. 
- Assault with a weapon: Section 267(a) of the Code. 
- Assault causing bodily harm: See assault causing bodily harm Section 267(b) of the Code. 
- Aggravated assault: Section 268 of the Code. 
- Assaulting a peace officer, etc.: Section 270 of the Code. 
- Sexual assault: Section 271 of the Code. 
- Sexual assault with a weapon or threats or causing bodily harm: Section 272 of the Code. 
- Aggravated sexual assault: See aggravated sexual assault.
An individual cannot consent to an assault with a weapon, assault causing bodily harm, aggravated assault, or any sexual assault. Consent will also be vitiated if two people consent to fight but serious bodily harm is intended and caused (R v Paice; R v Jobidon). A person cannot consent to serious bodily harm.
The Indian Penal Code covers the punishments and types of assault in Chapter 16,  sections 351 through 358.
Whoever makes any gesture, or any preparation intending or knowing it to be likely that such gesture or preparation will cause any person present to apprehend that he who makes that gesture or preparation is about to use criminal force to that person, is said to commit an assault.— s.351 of the Indian Penal Code 
The Code further explains that "mere words do not amount to an assault. But the words which a person uses may give to his gestures or preparation such a meaning as may make those gestures or preparations amount to an assault". Assault is in Indian criminal law an attempt to use criminal force (with criminal force being described in s.350). The attempt itself has been made an offence in India, as in other states.
The Criminal Code Act (chapter 29 of Part V; sections 351 to 365) creates a number of offences of assault.  Assault is defined by section 252 of that Act. Assault is a misdemeanor punishable by one year imprisonment; assault with "intent to have carnal knowledge of him or her" or who indecently assaults another, or who commits other more-serious variants of assault (as defined in the Act) are guilty of a felony, and longer prison terms are provided for. 
The offence of assault is created by section 113 of the Criminal Code.  A person is guilty of this offence if he unlawfully offers or attempts, with force or violence, to strike, beat, wound, or do bodily harm to, another.
Republic of Ireland
Section 2 of the Non-Fatal Offences against the Person Act 1997 creates the offence of assault, and section 3 of that Act creates the offence of assault causing harm.
South African law does not draw the distinction between assault and battery. Assault is a common law crime defined as "unlawfully and intentionally applying force to the person of another, or inspiring a belief in that other that force is immediately to be applied to him". The law also recognises the crime of assault with intent to cause grievous bodily harm, where grievous bodily harm is defined as "harm which in itself is such as seriously to interfere with health".  The common law crime of indecent assault was repealed by the Criminal Law (Sexual Offences and Related Matters) Amendment Act, 2007, and replaced by a statutory crime of sexual assault.
- Piracy with violence
- Section 2 of the Piracy Act 1837 provides that it is an offence, amongst other things, for a person, with intent to commit or at the time of or immediately before or immediately after committing the crime of piracy in respect of any ship or vessel, to assault, with intent to murder, any person being on board of or belonging to such ship or vessel.
- Assault on an officer of Revenue and Customs
- This offence (relating to officers of HMRC) is created by section 32(1) of the Commissioners for Revenue and Customs Act 2005.
- Assaulting an immigration officer
- This offence is created by of the UK Borders Act 2007.
- Assaulting an accredited financial investigator
- This section is created by section 453A of the Proceeds of Crime Act 2002. 
- Assaulting a member of an international joint investigation team
- This offence is created by of the Serious Organised Crime and Police Act 2005.
- Attacks on internationally protected persons
- Section 1(1)(a) of the Internationally Protected Persons Act 1978 (c.17) makes provision for assault occasioning actual bodily harm or causing injury on "protected persons" (including Heads of State).
- Attacks on UN Staff workers
- Section 1(2)(a) of the United Nations Personnel Act 1997 (c.13) makes provision for assault causing injury, and section 1(2)(b) makes provision for assault occasioning actual bodily harm, on UN staff.
- Assault by person committing an offence under the Night Poaching Act 1828
- This offence is created by section 2 of the Night Poaching Act 1828.
- Assault on customs and excise officers, etc.
- Section 16(1)(a) of the Customs and Excise Management Act 1979 (c.2) provided that it was an offence to, amongst other things, assault any person duly engaged in the performance of any duty or the exercise of any power imposed or conferred on him by or under any enactment relating to an assigned matter, or any person acting in his aid. For the meaning of "assault" in this provision, see Logdon v. DPP  Crim LR 121, DC. This offence was abolished and replaced by the Commissioners for Revenue and Customs Act 2005.
- Assaulting a person designated under section 43 of the Serious Organised Crime and Police Act 2005
- This offence was created by of the Serious Organised Crime and Police Act 2005. It related to officers of the Serious Organized Crime Agency and was repealed when that agency was abolished.
England and Wales
English law provides for two offences of assault: common assault and battery. Assault (or common assault) is committed if one intentionally or recklessly causes another person to apprehend immediate and unlawful personal violence. Violence in this context means any unlawful touching, though there is some debate over whether the touching must also be hostile. Confusingly, the terms "assault" and "common assault" often encompass the separate offence of battery, even in statutory settings such as s 40(3)(a) of the Criminal Justice Act 1988.
A common assault is an assault that lacks any of the aggravating features which Parliament has deemed serious enough to deserve a higher penalty. Section 39 of the Criminal Justice Act 1988 provides that common assault, like battery, is triable only in the magistrates' court in England and Wales (unless it is linked to a more serious offence, which is triable in the Crown Court). Additionally, if a Defendant has been charged on an indictment with assault occasioning actual bodily harm (ABH), or racially/religiously aggravated assault, then a jury in the Crown Court may acquit the Defendant of the more serious offence, but still convict of common assault if it finds common assault has been committed.
- Assault occasioning actual bodily harm
- The offence of assault occasioning actual bodily harm is created by section 47 of the Offences against the Person Act 1861.
- Assault with intent to rob
- The penalty for assault with intent to rob, a common law offence, is provided by section 8(2) of the Theft Act 1968.
- Racially or religiously aggravated common assault
- This offence is created by section 29(1)(c) of the Crime and Disorder Act 1998.
- Racially or religiously aggravated assault occasioning actual bodily harm
- This offence is created by section 29(1)(b) of the Crime and Disorder Act 1998.
- Assault with intent to resist arrest
- The offence of assault with intent to resist arrest is created by section 38 of the Offences against the Person Act 1861.
- Assaulting a constable in the execution of his duty
- Section 89(1) of the Police Act 1996 provides that it is an offence for a person to assault either:
- a constable acting in the execution of his duty; or
- a person assisting a constable in the execution of his duty.
- Assaulting a traffic officer
- This offence is created by of the Traffic Management Act 2004.
- Assaulting a person designated or accredited under sections 38 or 39 or 41 or 41A of the Police Reform Act 2002
- This offence is created by of the Police Reform Act 2002. Those sections relate respectively to persons given police powers by a chief police officer, detention contractors retained by police, accredited contractors under a community safety accreditation scheme, and weights and measures inspectors.
- Assault on a prison custody officer
- This offence is created by section 90(1) of the Criminal Justice Act 1991 (c.53).
- Assault on a secure training centre custody officer
- This offence is created by section 13(1) of the Criminal Justice and Public Order Act 1994 (c.33).
- Assault on officer saving wreck
- This offence is created by section 37 of the Offences against the Person Act 1861.
- Assaulting an officer of the court
- This offence is created by section 14(1)(b) of the County Courts Act 1984.
- Cruelty to persons under sixteen
- Section 1(1) of the Children and Young Persons Act 1933 provides that it is an offence for a person who has attained the age of sixteen years, and who has responsibility for a child or young person under that age, to, amongst other things, wilfully assault that child or young person, or to cause or procure that child or young person to be assaulted, in a manner likely to cause him unnecessary suffering or injury to health.
- Sexual assault
- The offence of sexual assault created by section 3 of the Sexual Offences Act 2003. It is not defined in terms of the offences of common assault or battery. It instead requires intentional touching and the absence of a reasonable belief in consent.
In Scots Law, assault is defined as an "attack upon the person of another".  There is no distinction made in Scotland between assault and battery (which is not a term used in Scots law), although, as in England and Wales, assault can be occasioned without a physical attack on another's person, as demonstrated in Atkinson v. HM Advocate  wherein the accused was found guilty of assaulting a shop assistant by simply jumping over a counter wearing a ski mask. The court said:
[A]n assault may be constituted by threatening gestures sufficient to produce alarm— Atkinson v. HM Advocate (1987)
Scottish law also provides for a more serious charge of aggravated assault on the basis of such factors as severity of injury, the use of a weapon, or Hamesuken (to assault a person in his own home). The mens rea for assault is simply "evil intent", although this has been held to mean no more than that assault "cannot be committed accidentally or recklessly or negligently" as upheld in Lord Advocate's Reference No 2 of 1992 where it was found that a "hold-up" in a shop justified as a joke would still constitute an offence.
It is a separate offence to assault on a constable in the execution of his duty, under Section 90, Police and Fire Reform (Scotland) Act 2012 (previously Section 41 of the Police (Scotland) Act 1967) which provides that it is an offence for a person to, amongst other things, assault a constable in the execution of his duty or a person assisting a constable in the execution of his duty.
Several offences of assault exist in Northern Ireland. The Offences against the Person Act 1861 creates the offences of:
- Common assault and battery: a summary offence, under section 42;
- Aggravated assault and battery: a summary offence, under section 43
- Common assault: under section 47
- Assault occasioning actual bodily harm: under section 47
The Criminal Justice (Miscellaneous Provisions) Act (Northern Ireland) 1968 creates the offences of:
- Assault with intent to resist arrest: under section 7(1)(b); this offence was formerly created by s.38 of the OAPA 1861.
That Act formerly created the offence of 'Assault on a constable in the execution of his duty'. under section 7(1)(a), but that section has been superseded by section 66(1) of the Police (Northern Ireland) Act 1998 (c.32) which now provides that it is an offence for a person to, amongst other things, assault a constable in the execution of his duty, or a person assisting a constable in the execution of his duty.
The term 'assault', when used in legislation, commonly refers to both common assault and battery, even though the two offences remain distinct. Common assault involves intentionally or recklessly causing a person to apprehend the imminent infliction of unlawful force, whilst battery refers to the actual infliction of force. 
Each state has legislation relating to the act of assault, and offences against the act that constitute assault are heard in the Magistrates Court of that state or indictable offences are heard in a District or Supreme Court of that State. The legislation that defines assault of each state outline what the elements are that make up the assault, where the assault is sectioned in legislation or criminal codes, and the penalties that apply for the offence of assault. 
In New South Wales, the Crimes Act 1900  defines a range of assault offences deemed more serious than common assault and which attract heavier penalties. These include:
Assault with further specific intent
- Acts done to the person with intent to murder 
- Wounding or grievous bodily harm 
- Use or possession of a weapon to resist arrest 
Assault causing certain injuries
- Actual bodily harm  - the term is not defined in the Crimes Act, but case law indicates actual bodily harm may include injuries such as bruises and scratches,  as well as psychological injuries  if the injury inflicted is more than merely transient (the injury does not necessarily need to be permanent)
- Wounding  - where there is breaking of the skin 
- Grievous bodily harm - which includes the destruction of a foetus, permanent or serious disfiguring, and transmission of a grievous bodily disease 
Four elements were required at common law:
- The apparent, present ability to carry out;
- An unlawful attempt;
- To commit a violent injury;
- Upon another.
Simple assault can be distinguished without the intent of injury upon another person. The violation of one's personal space or touching in a way the victim deemed inappropriate can be simple assault. In common law states an assault is not committed by merely, for example, swearing at another; without threat of battery, there can be no assault.
As the criminal law evolved, element one was weakened in most jurisdictions so that a reasonable fear of bodily injury would suffice. These four elements were eventually codified in most states.
Laws on assault vary by state. Since each state has its own laws, there is no universal assault law. Acts classified as assault in one state may be classified as battery, menacing, intimidation, reckless endangerment etc. in another state. Modern American statutes may define assault as including:
- an attempt to cause or purposely, knowingly, or recklessly causing bodily injury to another
- negligently causing bodily injury to another with a dangerous weapon (assault with a deadly weapon). 
- causing bodily harm by reckless operation of a motor vehicle (vehicular assault). 
- threatening another in a menacing manner. 
- knowingly causing physical contact with another person knowing the other person will regard the contact as offensive or provocative 
- causing stupor, unconsciousness or physical injury by intentionally administering a drug or controlled substance without consent 
- purposely or knowingly causing reasonable apprehension of bodily injury in another 
- any act which is intended to place another in fear of immediate physical contact which will be painful, injurious, insulting, or offensive, coupled with the apparent ability to execute the act. 
The laws on assault differ significantly from state to state as exemplified below.
- (a) A person commits assault who:
- (1) Intentionally, knowingly or recklessly causes bodily injury to another;
- (2) Intentionally or knowingly causes another to reasonably fear imminent bodily injury; or
- (3) Intentionally or knowingly causes physical contact with another and a reasonable person would regard the contact as extremely offensive or provocative.
Assault is intentionally placing another person in reasonable apprehension of immediate bodily harm.
- A person is guilty of an offense if that person:
- Willfully causes bodily injury to another human being; or
- Negligently causes bodily injury to another human being by means of a firearm, destructive device, or other weapon, the use of which against a human being is likely to cause death or serious bodily injury.
States vary on whether it is possible to commit an "attempted assault" since it can be considered a double inchoate offense.
In some states, consent is a complete defense to assault. In other jurisdictions, mutual consent is an incomplete defense, with the result that the misdemeanor is treated as a petty misdemeanor.
In New York State assault as defined in the New York State Penal Code Article 120,  requires an actual injury. Other states define this as battery. There is no crime of battery in New York. The threat of imminent injury without physical contact in New York is called menacing. New York also has specific laws against hazing when such threats are made as requirement to join an organization.
Furthermore, the crime of assault generally requires that both the perpetrator and the victim of an assault be human. Thus, there is no assault if an ox gores a man. However, the Unborn Victims of Violence Act of 2004 treats the fetus as a separate person for the purposes of assault and other violent crimes, under certain limited circumstances. See
Some possible examples of defenses, mitigating circumstances, or failures of proof are:
- A defendant could argue that since he was drunk, he could not form the specific intent to commit assault. This defense would most likely fail since only involuntary intoxication is accepted as a defense in most American jurisdictions.
- A defendant could also argue that he was engaged in mutually consensual behavior.
Assault in Ancient Greece was normally termed hubris. Contrary to modern usage, the term did not have the extended connotation of overweening pride, self-confidence or arrogance, often resulting in fatal retribution. In Ancient Greece, "hubris" referred to actions which, intentionally or not, shamed and humiliated the victim, and frequently the perpetrator as well. It was most evident in the public and private actions of the powerful and rich.
Violations of the law against hubris included what would today be termed assault and battery; sexual crimes ranging from forcible rape of women or children to consensual but improper activities; or the theft of public or sacred property. Two well-known cases are found in the speeches of Demosthenes, a prominent statesman and orator in ancient Greece. These two examples occurred when first, Meidias punched Demosthenes in the face in the theater (Against Meidias), and second when (in Against Konon) a defendant allegedly assaulted a man and crowed over the victim.
Hubris, though not specifically defined, was a legal term and was considered a crime in classical Athens. It was also considered the greatest sin of the ancient Greek world. That was so because it not only was proof of excessive pride, but also resulted in violent acts by or to those involved. The category of acts constituting hubris for the ancient Greeks apparently broadened from the original specific reference to mutilation of a corpse, or a humiliation of a defeated foe, or irreverent, "outrageous treatment", in general.
The meaning was eventually further generalized in its modern English usage to apply to any outrageous act or exhibition of pride or disregard for basic moral laws. Such an act may be referred to as an "act of hubris", or the person committing the act may be said to be hubristic. Atë, Greek for 'ruin, folly, delusion', is the action performed by the hero, usually because of his/her hubris, or great pride, that leads to his/her death or downfall.
Crucial to this definition are the ancient Greek concepts of honor (timē) and shame. The concept of timē included not only the exaltation of the one receiving honor, but also the shaming of the one overcome by the act of hubris. This concept of honor is akin to a zero-sum game. Rush Rehm simplifies this definition to the contemporary concept of "insolence, contempt, and excessive violence".