Learn Farsi: مهاجم و مدافع چابک دویدند. - The striker and the defender ran nimbly.

In Farsi, you can often use a plain adjective like چابک (nimble/agile) as an adverb to describe how an action is done. We know it's acting as an adverb modifying the verb دویدند (they ran) because it isn't connected to the noun مدافع (defender) with an ezafe (the connecting "e" sound). If it meant "the nimble defender", it would be مدافعِ چابک (modafe'-e chabok).

Are the words مهاجم and مدافع strictly sports terms?

They are very commonly used in sports like football (soccer) to mean "striker/forward" and "defender", but they aren't limited to sports. They are also standard formal or military terms for "attacker" and "defender".

Why does the verb دویدند end in ـند (-and)?

The verb must match the subject. Since there are two people doing the running—مهاجم و مدافع (the striker and the defender)—the subject is plural ("they"). Therefore, the past tense verb دوید (he/she ran) takes the third-person plural ending ـند to become دویدند (they ran).

How should the و (and) be pronounced in this sentence?

In everyday spoken Farsi, the conjunction و is almost always pronounced as a quick "o" sound that attaches to the word before it. Instead of saying "va", you would naturally pronounce this phrase as mohajem-o modafe'.