Learn Farsi: پلیس زدوخورد را سریع تمام کرد.

It is formed by combining the past stems of two verbs with the conjunction o (and). zad is the past stem of zadan (to hit), and khord is the past stem of khordan (which means to eat, but also to be hit or collide). Together, literally hit and be hit, they create the abstract noun for a brawl or clash.

Why is the و in the middle of زدوخورد pronounced as "o" instead of "va"?

In coordinate compound nouns like this one, the conjunction meaning "and" is always pronounced as a short "o" rather than "va". Because the combination forms a single new concept, it is also usually written together as a single block without spaces.

Since زدوخورد is made of two verb stems, how can it take the direct object marker را (râ)?

Once combined, zad-o-khord functions entirely as a regular noun. Because the brawl is the specific thing being finished by the police, the whole compound acts as the definite direct object, and so râ is placed immediately after it just like with any other noun.

Why is the verb تمام کرد (tamâm kard) in the singular form when the police usually implies multiple officers?

In Farsi, collective nouns like polis (police) or artesh (army) typically take a singular verb when they are acting together as a single institution or unit, just as they do in this sentence.