Takım kaptanı yarışmacıları tanıttı.

Because takım kaptanı is a Turkish noun compound meaning team captain. In this pattern, the second noun usually takes the 3rd-person possessive ending:

• takım = team
• kaptan-ı = captain + compound/possessive ending

So takım kaptanı literally looks a bit like the captain of the team, but in natural English it is simply the team captain. It does not automatically mean his/her captain here.

Because yarışmacıları has the accusative ending, which marks the direct object. That makes takım kaptanı the subject.

So the structure is:

• Takım kaptanı = subject
• yarışmacıları = object
• tanıttı = verb

That -ı is the accusative ending on a plural noun:

• yarışmacı = contestant
• yarışmacılar = contestants
• yarışmacıları = the contestants / the contestants as a specific direct object

In Turkish, a specific or definite direct object is usually marked with the accusative. That is why this means introduced the contestants, not just introduced contestants in a vague sense.

Yes. On its own, yarışmacıları can be ambiguous. Depending on context, it can mean:

• the contestants
• his/her contestants
• sometimes their contestants

In this sentence, the natural reading is the contestants, because it fits the sentence structure as the direct object.

Turkish does not have articles like English the and a/an. Instead, definiteness is shown through context and grammar.

Here, yarışmacıları is understood as definite partly because it has the accusative ending, so Turkish can express the contestants without a separate word for the.

Tanıttı is the simple past, 3rd-person singular:

• dictionary form: tanıtmak = to introduce
• stem: tanıt-
• past ending: -tı

So tanıttı means he/she introduced. Turkish does not need a separate word for he or she here; the subject is already given as takım kaptanı.

Because the verb stem already ends in t:

• tanıt-

And the past suffix here also begins with t:

• -tı

So:

• tanıt + tı = tanıttı

The double tt is normal and not a spelling mistake.

Because Turkish normally uses Subject – Object – Verb order. This sentence follows that standard pattern:

• Takım kaptanı = subject
• yarışmacıları = object
• tanıttı = verb

English usually prefers Subject – Verb – Object, so Turkish word order often feels reversed to English speakers.

Yes. They are related:

• tanımak = to know / recognize
• tanıtmak = to introduce / make known

So tanıtmak has a make someone know someone/something idea behind it. That is why it means introduce.

The Turkish letter ı is the dotless i. It is a separate vowel from i, and English does not have a perfect equivalent.

A few tips:

• keep your tongue farther back than for English ee
• do not pronounce it like eye
• it is a short back vowel

Very rough approximations:

• kaptanı ≈ kahp-tah-nuh
• tanıttı ≈ tah-nuht-tuh

These are only approximations, but they can help you get started.