The most common and most likely answer to this crossword clue is the 3 letter word LAW
I've seen this crossword clue in Independent
L
A
W
Buddy explains!
The straight part
We know that "rules" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rules = law.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LAW mean?
LAW noun- The body of binding rules and regulations, customs and standards established in a community by its legislative and judicial authorities.
- A binding regulation or custom established in a community in this way.
- (more generally) A rule, such as:
- The control and order brought about by the observance of such rules.
- A person or group that act(s) with authority to uphold such rules and order (for example, one or more police officers).
- The profession that deals with such rules (as lawyers, judges, police officers, etc).
- Jurisprudence, the field of knowledge which encompasses these rules.
- Litigation, legal action (as a means of maintaining or restoring order, redressing wrongs, etc).
- An allowance of distance or time (a head start) given to a weaker (human or animal) competitor in a race, to make the race more fair.
- One of two metaphysical forces ruling the world in some fantasy settings, also called order, and opposed to chaos.
- An oath sworn before a court, especially disclaiming a debt. (Chiefly in the phrases "wager of law", "wage one's law", "perform one's law", "lose one's law".)
- To work as a lawyer; to practice law.
- To prosecute or sue (someone), to litigate.
- To rule over (with a certain effect) by law; govern.
- To enforce the law.
- To subject to legal restrictions.
- A tumulus of stones.
- A hill.
- An exclamation of mild surprise; lawks.