Learn Farsi: مدافع دارد بی‌نقص بازی می‌کند.

This is exactly how Farsi handles adverbs of manner! You can often take a regular adjective like بی‌نقص (flawless) and use it unmodified to describe an action. Because it is placed right before the verb بازی می‌کند (is playing), it tells us how the defender is playing, acting just like an English adverb ending in "-ly".

Why is the adverb بی‌نقص placed right in the middle of the verb phrase?

The verb "is playing" is in the present continuous tense, which is built with a helper verb (دارد) and a main verb (بازی می‌کند). In Farsi, adverbs of manner usually sit directly before the main verb. As a result, the adverb naturally gets sandwiched between the helper verb and the main compound verb.

How does the prefix work in the word بی‌نقص?

It is formed by combining the prefix بی‌ (meaning "without") and the noun نقص (meaning "flaw", "defect", or "imperfection"). Attaching بی‌ to a noun is a very common way to build adjectives in Farsi, functioning exactly like the English suffix "-less".

Since بازی می‌کند is a compound verb, could we split it and put the adverb inside, like دارد بازی بی‌نقص می‌کند?

While you will occasionally see other words slip inside compound verbs, adverbs of manner generally do not break them up. It is much more natural to keep the compound verb بازی می‌کند intact and place the adverb right before it.