Learn Italian: Chiunque può vincere questo concorso.

Just like "anyone" or "whoever" in English, the Italian pronoun chiunque is grammatically singular. You must always pair it with a third-person singular verb.

What is the difference between using chiunque and qualcuno here?

Chiunque means "anyone" (meaning any person at all has the ability to win). If you used qualcuno, the sentence would mean "Someone can win this competition", which implies a specific but unnamed person, rather than absolutely anybody.

I've heard that chiunque requires the subjunctive. Why is può in the indicative mood?

Chiunque only triggers the subjunctive when it means "whoever" and introduces a dependent relative clause (for example, "I will congratulate whoever wins"). In this sentence, it just means "anyone" and acts as the main subject of a standalone sentence, so it takes the normal indicative mood.

Does concorso refer to any kind of competition, like a football tournament?

Not usually. A concorso is typically a prize draw, a contest, or a formal competitive examination (like applying for a government job). For sports matches or athletic events, you would normally use words like gara, partita, or competizione.