Punching, kicking, slapping and slashing is a coordinated subject requiring the plural verb are. When or replaces and, the case is different. In your example, it isn’t clear whether slashing is seen as an alternative to the other three actions, or whether each is an alternative. If just one of those actions performed on its own is strictly prohibited, then the single verb is might emphasise the fact. If it is only more than one committed together that is strictly prohibited, then you might want the plural.
You will see that the sentence as it stands is open to several interpretations. A legal document normally needs to eliminate any such ambiguity as far as possible. For that reason, I think the best advice would be for you to have the document drafted by someone who has qualifications and experience in this kind of work.