How can you tell whether 'zostać' means 'to become' versus 'to stay' in a given context?
„Zostać” as in "to become" always comes with an object noun in instrumental case.
And what is the case that accompanies 'to stay'? Like if you were to stay a police officer?
Ah, you meant that kind of "stay", when a person is already a policeman and will continue to do so? Then I would suggest using verbs like "pozostać", or "nadal być".
Okay that's good to know, thanks!