Is a question of whether or not an action is considered "cheating" in a game within the parameters of the law exchange? If not, which stack exchange site might help me with a question as to the game of billiards?
Apart from Board and Card Games, there is a remote chance that it could be on-topic for Philosophy, provided that you could reduce the matter to a logical inference (the question would be whether the inference is consistent with the game premises). Cheating is immoral, and ethics is a well-known branch of philosophy, which open up another way of framing the question.
Depends what you mean by cheating and what games you are talking about.
For sport (and board/card games), in general, questions about the rules "on the field" would be off-topic but questions about the conduct and structure of competitions would generally be fine - these take place within the legal framework of the country and cheating would be lawbreaking.
Indeed, there is a specific international tribunal which most jurisdictions recognise as a body that can handle mediations and arbitrations on this matter: the Court of Arbitration for Sport
You could try the Board & Card Games or Role Playing Games stacks as applicable.
Questions about or involving the application of (national or international) law or legal process or legal expertise to the realm of sports, are on-topic for Law Stack Exchange.
questions about the America's Cup yacht race series: the rules are (vigorously) arbitrated by a court in New York, involving a legal process and legal expertise, and are likely to be on-topic.
questions regarding appeals to the Court of Arbitration for Sport: these invoke and involve a legal process and legal expertise, and are likely to be on-topic.
questions about the (alleged or actual) crimes of a sportsperson (be they real or hypothetical): the sport is only tangential, while the question is clearly about some aspect of law, and are likely to be on-topic.
questions about laws and regulations, contracts and terms which apply to a game or games (e.g. casino gaming, live tournaments or online play of other games): these are similarly a question about aspects of law where the law happens to deal with games. However, check that they aren't already answered under more general terms.
Questions about the interpretation of a rule or law in a sport, board or card game, or other competitive environment is off-topic for Law Stack Exchange. However, it may well be on-topic for another Stack Exchange website, such as
Note that your question may straddle more than one SE site (it is potentially on-topic for both, to greater or lesser extent), or it may fall in the gap between two or several of them (it is on-topic for none/is off-topic for all). Specific queries about whether a given question is on-/off-topic, should be directed to the appropriate meta.
Some games have quite legalistic rules and ways of handling alleged rules violations. Bridge, for instance, is governed by a set of formal "Laws" and even has an appeals process in some cases. In one famous case of alleged cheating, the evidence was actually reviewed by a senior Judge (from the UK's High Court if I recall correctly) who made a decision based on a legal analysis of the sufficiency of the evidence.
Nevertheless, such rules and procedures are not considered on-topic here. Some will be on-topic on other SE sites, such as Board and Card Games. Others will not fit any SE site. Other answers have already suggested several such possible sites.