Learn Russian: Полиция штрафует водителей, потому что они игнорируют правила. - The police fine drivers because they ignore the rules.

Both штрафовать (to fine) and игнорировать (to ignore) belong to a special group of verbs. When you conjugate them in the present tense, the -ова- suffix drops out and is replaced by -у- (or -ю-). That is why we get штрафует (he/she/it fines) instead of "штрафовает", and игнорируют (they ignore) instead of "игнорировают".

The English translation says "The police fine" (plural), but the Russian verb штрафует is singular. Why?

In Russian, полиция is a singular feminine noun, much like "the police force" or "the police department" in English. Therefore, it takes singular verb endings, like штрафует. In English, we treat "police" as a plural noun, which is why the translation says "fine" instead of "fines".

Why is the word for drivers водителей instead of "водители"?

The police are fining the drivers, making them the direct object of the sentence. This means we need the accusative case. Because водитель (driver) is an animate noun (a living person), its accusative plural form looks exactly like its genitive plural form: водителей.

Since водителей changed for the accusative case, why doesn't правила change?