Learn Polish: Nie strzelaj! Policja już jedzie. - Don't shoot! The police are already coming.

In Polish, negative commands (telling someone not to do something) almost always take the imperfective aspect. This applies even if you are trying to stop a single, sudden action from happening right now. So, nie strzelaj is the standard and correct way to say "don't shoot!".

The English translation says "The police are", but policja takes a singular verb here. Do we ever use a plural form?

The word policja is a singular feminine noun referring to the institution or the force as a whole, which is why it uses the singular verb jedzie. English treats "police" as a plural noun, but Polish doesn't. If you want to refer to multiple individual officers on the scene, you would use the plural noun policjanci.

Why use jedzie instead of a general word for "arriving" or "coming"?

Polish is very specific about how movement happens. Because the police are coming in vehicles, you must use a verb for driving or riding. Jedzie is the determinate (one-way) imperfective verb of motion, which perfectly captures the idea that they are currently in transit to this specific location.

Doesn't już literally mean "already"? How does that work with an action happening right now?

Yes, już means "already", but in Polish it is used very often with present tense verbs to emphasize that an action is currently underway. Saying już jedzie stresses that the police have already departed and are actively on their way right now.