Are questions about "rules of sport or games" on-topic here
It depends on the type of question.
Questions that reduce to "how to play?", "what is the best strategy/move in this situation?", "why is this move/player granted n points?", and so forth, certainly would be off-topic even if an OP prefixes them with "According to the rules of the game, [...]". That is because they mostly involve game expertise rather than tenets of legal construction & rationale.
By contrast, other types of questions are within scope of LawSE. Rules of a game can be relevant to assessing whether a claim sounds in violation of due process and/or whether doctrines of consent or of assumption of risk precludes that claim. For instance, Avila v. Citrus Comm. College Dist, 41 Cal.Rptr.3d 299, 312 (2006) ponders whether legal liability arises from "conduct that violates the rules of the game". There, the Concurring & Dissenting opinion even resorts to common practice as well as official commentary to the rules of the game to support a number of arguments, Id. at 316, 318.
Similarly, Thompson v. McNeill, 53 Ohio St.3d 102, 105 (1990) states:
If the rules of a sport allow conduct intended to harm another player,
as they do in boxing or football, for example, it follows that those
same rules also allow behavior that would otherwise give rise to
liability for recklessness. But any conduct which is characterized by
the strong probability of harm that recklessness entails, and which
occurs outside the normal conduct and customs of the sport, may give
rise to liability.
This implies a scrutiny of the rules of a sport or game can be crucial for determining whether the conduct at issue is actionable or protected by the doctrine of primary assumption of risk, which Al-Jahmi v. Ohio Athletic Comm. 2022-Ohio-2296 (June 30, 2022), describes as follows:
[A] plaintiff who voluntarily engages in a recreational activity or
sporting event assumes the inherent risks of that activity and cannot
recover for injuries sustained in engaging in the activity unless the
defendant acted recklessly or intentionally in causing the injuries.
Lastly, the involvement of specific terminology or knowledge tends to constrain who is capable of answering a question, but an increase of requisite specialization does not in and of itself render that question off-topic.