At common law, an assembly of three or more people is an ‘unlawful assembly’ if it is carried out with the intention to commit a crime by open force or to carry out any lawful or unlawful common purpose in a manner that gives firm and courageous people in the neighbourhood reasonable grounds to apprehend a breach of the peace (R v O’Sullivan (1948) 48 SR (NSW) 400; 65 WN (NSW) 155; see also Black v Corkery (1988) 33 A Crim R 134).
A lawful assembly of three or more people may become unlawful if a proposal is made to it to commit a violent act which will disturb the public peace, and that proposal is acted on (R v O’Sullivan (1948) 48 SR (NSW) 400; 65 WN (NSW) 155; see also Black v Corkery (1988) 33 A Crim R 134).
An ‘unlawful assembly’ becomes a ‘rout’ as soon as the assembled persons do anything toward carrying out the illegal common purpose which makes their assembly unlawful. A ‘rout’ becomes a ‘riot’ when this illegal purpose is forcibly effected by persons mutually intending to resist any opposition (Halsbury's Laws of England (4th ed, 1976) Vol 11, paras 856-862).
Riots, routs and unlawful assembly distinguished
It is suggested that the distinction between a riot, rout and unlawful assembly is that a riot is a tumultuous meeting of people who are guilty of actual violence; a rout occurs where such people try to commit an act that would make them rioters; and an unlawful assembly occurs where such people meet intending to make a riot, but neither carry their purpose into effect, nor make any attempt to.
Like an affray, a riot involves both violence and public alarm. They involve public alarm because they are currently or potentially dangerous.
For an accused to be guilty of riot, the following five elements must be satisfied simultaneously:
Three or more people assembled, of which the accused is one;
At least three of these people, including the accused, had a common purpose;
The assembled people, including the accused, embarked on executing that common purpose;
The people who had the common purpose intended to help each other, by force if necessary, against any person who may oppose them in the execution of their common purpose, and the accused also intended to provide such help; and
The people who had the common purpose used such violence as would alarm at least one person of reasonable firmness and courage (R v McCormack  VR 104; Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198; Cook, Hartigan and McCarr v R  2 Qd R 77; Boxer v R (1995) 14 WAR 505).
The requirement of a common purpose means that participants in a riot may be jointly charged only if they were contemporaneously involved in the alleged riot (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
A jury may find an accused guilty of rout or unlawful assembly as alternative verdicts to riot if the prosecution fails to prove all the essential elements of riot (R v Wright (1994) 74 A Crim R 152; R v Cook  2 Qd R 77; Boxer v The Queen (1995) 14 WAR 505).
Three or more people assembled
The first element that the prosecution must prove is that there were three or more persons assembled, and that the accused was one of those persons.
All alleged participants must be present at the scene of the riot at the same time, unless they incited the riot that subsequently ensued in their absence (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198; see also R v Sharpe (1848) 3 Cox CC 288; R v Caird (1970) 54 Cr App R 499).
Thus, when several accused are alleged to have committed the same offence of riot and one leaves the scene, they cannot be jointly guilty of the offence from the time that person leaves (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
The exception to this is where an accused encourages or incites the others to continue the riot, even though he or she has left the scene. In that instance, the accused may be charged as a principal along with the others (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198; see also R v Sharpe (1848) 3 Cox CC 288).
Where a crowd temporarily disperses, but a significant number of them later reassemble, valid charges of riot may still be brought (Tomarchio v Pocock  WASCA 156).
For a common purpose
The second element is that at least three persons, one of which must be the accused, must have been assembled for a common purpose.
The common purpose may be lawful or unlawful (Cunninghame, Graham and Burns (1888) 16 Cox CC 420).
It may also be a private or public or political purpose (O'Brien v Friel  NI 29).
The common purpose cannot be constituted by continuing the riot itself. Thus, it is not sufficient to prove a common purpose to show that, once a riot has commenced and extended over a period of time, people, otherwise than peaceably, joined the assembly and participated in it (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
Who embark on executing that common purpose
The third element requires those persons to have embarked on that common purpose (Field ν The Receiver of the Metropolitan Police  2 KB 853).
For an accused to be guilty of the offence of riot, he or she must have been involved in at least some of the activity that makes the assembly a riot (R v Wright (1994) 74 A Crim R 152; R v Cook  2 Qd R 77; Boxer v The Queen (1995) 14 WAR 505).
Whether a particular accused is sufficiently involved is a question for the jury (R v Cook  2 Qd R 77).
However, it has been suggested that, where the behaviour that is alleged to make an assembly a riot is comprised of the assembly moving in a threatening way, the accused must participate in such movement. If the alleged behaviour is made up of several elements, such as movement, threats and property damage, it would be sufficient for the accused to be involved in some of that activity (R v Cook  2 Qd R 77; see also R v Thomas  1 Qd R 323).
Where some, but not all, of the members of a group that is unlawfully assembled engage in riotous behaviour, only those who actively engage in such behaviour will be guilty of the offence of riot (R v Cook  2 Qd R 77).
Intending to help each other by force if necessary
The next element that needs to be proved requires the assembled persons to have intended to help each other by force if necessary (Field ν The Receiver of the Metropolitan Police  2 KB 853; see also R v Murray (1992) 16 Crim LJ 273).
The accused must also have individually had that same intent to help the other members of the group by force if necessary.
It has been noted that this element means that it is difficult to envisage a situation where a person can be guilty of the same offence of riot as another person unless at some point in time they were present together in the assembly (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
Therefore, if several accused are charged with the one offence of riot, they each must have had both a common purpose and intention to help each other, by force if necessary, against any person who might oppose them in execution of that common purpose (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
Who use such violence to alarm at least one person of reasonable firmness and courage
The final element requires those persons to use such violence to alarm at least one person of reasonable firmness and courage.
It is doubtful that this requires a real person to be alarmed. The better view is that the violence must be of such a level that a hypothetical bystander of reasonable firmness and courage would be put in fear by the display (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198; see also J W Dwyer Ltd v Metropolitan Police District Receiver  2 QB 970; Kamara v Director of Public Prosecutions  AC 104).
The assembly of persons becomes riotous at the latest when alarming force or violence begins to be used (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
The alleged force and violence needs to occur simultaneously with the execution of the common purpose. Therefore, if a group of three or more assemble together for a common purpose and incidentally display force and violence, but then peacefully set out to execute the common purpose, no offence of riot will have been committed. However, they could be guilty of participating in an unlawful assembly (Anderson v Attorney-General (NSW) (1987) 10 NSWLR 198).
It has been suggested that the degree of force required to be displayed to constitute the offence of riot must be ‘so tumultuous … as to disturb the peace’ (Boxer v The Queen (1995) 14 WAR 505).
This does not necessarily require physical violence, personal injury or property damage. It only requires ‘tumult’, which has been interpreted as involving several people being involved in agitated movement, or an excited and emotionally aroused assembly of people, which is usually (although not necessarily) accompanied by noise (R v Thomas  1 Qd R 323; see also Boxer v The Queen (1995) 14 WAR 505; J W Dwyer Ltd v Metropolitan Police District Receiver  2 QB 970).