Hmm. I've never heard 'ruling' in that context before (i.e., 'A person wants to ask the ruling about slapping a policemen'). We shall await further responses from natives, I suppose. 👁 Big Grin :D
A ruling is a decision handed down by a court.
A law is a rule that applies to everyone.
A rule is a law that applies within, for example, a sports club.
A penalty is a punishment for breaking a law or a rule.
So, what are you trying to say?
What is the law on slapping a policeman?
What is the penalty for slapping a policeman?