The phrase "against the rules" means to go against a set of established guidelines, principles or standards. It is used in various contexts such as in sports where certain behaviors are prohibited and considered unfair play; in schools where there are codes of conduct that students must follow; in workplaces where company policies dictate what is acceptable behavior; and even in social situations where there are unwritten rules governing appropriate behavior. When someone breaks the "rules," they are going against what is expected or permitted, which may result in consequences such as penalties, reprimands, or loss of privileges.