El concursante compite con el contrincante.

Compite is the third-person singular present indicative form of competir.

• competir = the infinitive, to compete
• compite = he/she competes or it competes

It matches el concursante, which is singular.

A quick mini-conjugation:

• yo compito
• tú compites
• él/ella compite
• nosotros competimos
• vosotros competís
• ellos/ellas compiten

Notice that competir is a stem-changing verb in some forms: e → i
So:

• competes becomes compites
• compete becomes compite

but:

• competimos stays competimos

Because both nouns refer to specific people: the contestant and the opponent.

In Spanish, the definite article is used very naturally with specific roles or people:

• el concursante
• el contrincante

English sometimes leaves articles out in places where Spanish does not, but here Spanish normally includes them.

They are related, but they are not the same word.

• concursante = contestant
• contrincante = opponent, rival

So concursante tells you the person is taking part in a contest or competition, while contrincante highlights the other person as the one they are facing.

In some contexts, both people could be called concursantes, but from the point of view of one person, the other can be called el contrincante.

With competir, Spanish very commonly uses con:

• competir con alguien = to compete with / against someone

Even though English often says against, Spanish often prefers con with this verb.

Contra is possible in some contexts, especially when you want to stress direct opposition, but competir con is very standard and natural.

So:

• compite con el contrincante = natural, standard Spanish
• compite contra el contrincante = understandable, but less neutral here

No. Both are usually common-gender nouns. That means the noun itself stays the same, and the article shows the gender.

• el concursante = the male contestant
• la concursante = the female contestant
• el contrincante = the male opponent
• la contrincante = the female opponent

So if both were women, you could say:

• La concursante compite con la contrincante.

It is stem-changing, which is a type of irregularity.

The e in the stem changes to i in stressed forms:

• yo compito
• tú compites
• él/ella compite
• ellos compiten

But not in:

• nosotros competimos
• vosotros competís

So it is not completely irregular, but it does not behave like a fully regular -ir verb.

Because el contrincante is not a direct object here. It comes after the preposition con.

The personal a is used mainly with animate direct objects:

• Veo al contrincante. = I see the opponent.

But here the structure is:

• compite con el contrincante

Since con is already there, you do not add a personal a.

Yes, Spanish word order is more flexible than English word order, although this sentence is the most neutral version:

• El concursante compite con el contrincante.

That is a normal subject + verb + complement order.

You could rearrange parts for emphasis, but it would sound less neutral, for example:

• Con el contrincante compite el concursante.

This kind of change is possible, but the original sentence is the best basic pattern for learners.

Sometimes yes, but the nuance changes.

• concursante = contestant, especially in a contest, competition, or game show
• competidor = competitor, a broader term

So if you are talking about a TV contest or a formal contest, concursante is often the better word.
If you are speaking more generally about someone who competes, competidor may fit better.

Similarly, for contrincante, possible alternatives include:

• rival
• oponente

But each has its own tone and usage.

Not necessarily. The Spanish present tense can mean different things depending on context.

El concursante compite con el contrincante could mean:

• the contestant competes with the opponent, in general
• the contestant is competing with the opponent, depending on context

If you want to make the right now meaning clearer, Spanish often uses:

• El concursante está compitiendo con el contrincante.

So the simple present can be general or current, and context decides.