Ο αντίπαλος παίζει καλά.

Ο is the masculine singular definite article. It works like the in English.

So ο αντίπαλος is a full noun phrase meaning the opponent. In Greek, the definite article is used very often, including in places where English might sometimes leave it out.

It is masculine, singular, nominative.

• ο = nominative masculine singular article
• αντίπαλος = nominative masculine singular noun

It is in the nominative because it is the subject of the sentence, the person doing the action.

Here it is being used as a noun.

But αντίπαλος can also function as an adjective in Greek, with the sense of opposing or rival depending on context. In this sentence, though, it clearly means opponent/rival, so it is acting as a noun.

Παίζει is the 3rd person singular present form of παίζω.

That means it matches he/she/it or a singular noun like ο αντίπαλος.

So grammatically, it tells you:

• person: 3rd
• number: singular
• tense: present

It can mean either, depending on context.

Greek present tense often covers both:

• plays
• is playing

So without more context, παίζει could describe a general ability or a current action.

Because καλά is an adverb, not an adjective.

Here it modifies the verb παίζει, so it tells you how the opponent plays.

Compare:

• καλός / καλή / καλό = adjective, used to describe a noun
• καλά = adverb, used to describe a verb

So:

• ο καλός αντίπαλος = the good opponent
• παίζει καλά = plays well

Yes. Greek word order is more flexible than English word order.

The sentence Ο αντίπαλος παίζει καλά is a very neutral, standard order. But you could also hear:

• Παίζει καλά ο αντίπαλος.
• Καλά παίζει ο αντίπαλος.

These alternatives can shift the emphasis a little. Greek often uses word order for focus and style, not just basic grammar.

Still, for a learner, Ο αντίπαλος παίζει καλά is the safest and most neutral version.

In normal Greek, you would usually keep the article here.

Ο αντίπαλος παίζει καλά sounds natural for the opponent plays well.

Without the article, Αντίπαλος παίζει καλά, it sounds unnatural in ordinary speech unless there is some very special context, such as a headline, notes, or highly compressed style.

A simple pronunciation guide is:

o an-DI-pa-los PE-zi ka-LA

More closely:

• ο = o
• αντίπαλος = an-DI-pa-los
• παίζει = PE-zi
• καλά = ka-LA

A few useful pronunciation points:

• the stress is on -τί-, παί-, and -λά
• αί in παίζει sounds like e
• ει in παίζει sounds like i

So παίζει sounds roughly like PE-zi, not pai-zei.

The accent marks show which syllable is stressed.

So:

• αντίπαλος → stress on τί
• παίζει → stress on παί
• καλά → stress on λά

Stress matters in Greek pronunciation, so the written accent is very important.

A common way to say that is:

Η αντίπαλος παίζει καλά.

The article changes from ο to η. In this use, αντίπαλος can stay the same.

So the main change is the article:

• ο αντίπαλος = masculine
• η αντίπαλος = feminine

For a negative sentence, add δεν before the verb:

Ο αντίπαλος δεν παίζει καλά.

For a yes/no question, Greek often uses the same words and relies on intonation in speech:

Ο αντίπαλος παίζει καλά;

You may also hear:

Παίζει καλά ο αντίπαλος;

So the main ideas are:

• δεν makes it negative
• intonation usually makes it a question