Question

Billy throws rocks. each time he throws a rock, he is immediately spanked. spanking is a ________.

Answer 1

A punishment of course. If his parents tell him not to throw rocks, and tell him the consequences of doing it again it's a punishment. That teaches him before he hurts someone, breaks something or hurts himself.

Answer 2

the answer to this question is Punishment
punishment refers to the penalty that given to a certain someone if that person is not complying to a certain rules/standard.
The purpose of punishment is to discourage that person from repeating that action again unless they're prepared for the consequences.