Learn Turkish: Müsabakadan önce kullanmaması gereken o yasaklı hormon dopingdir. - That banned hormone that he must not use before the competition is doping.

The first -ma is the negative suffix (not), and the second -ma creates a verbal noun (acting like an English gerund). When attached to the verb root kullan- (use) and the third-person possessive -sı (his/her), it literally means "his/her not using."

How does kullanmaması combine with gereken to mean "that he must not use"?

To form an adjective clause about a necessity, Turkish pairs a possessive verbal noun with gereken (the subject participle of gerek, meaning "which is necessary"). So, kullanmaması gereken hormon translates literally as "the hormone which his-not-using is necessary."

Why is the word yasaklı used here instead of just yasak for "banned"?

Yasak means "forbidden" and usually acts as a noun or predicate to state a rule (like girmek yasak - entry is forbidden). Yasaklı, however, means "having a ban" and is used as an adjective for a noun placed on a restricted list, like a banned player or a banned hormone.

What nuance does the -dir suffix add to dopingdir?

While it functions as the "is" in the sentence, the -dir suffix here adds a formal, definitive, or encyclopedic tone. It signals that this statement is an official rule or an objective definition, typical of what you would find in a sports regulation book.