Αυτό το σχόλιο ήταν προσβολή.

Because σχόλιο is a neuter singular noun, and the demonstrative αυτό has to agree with it in gender and number.

• masculine: αυτός
• feminine: αυτή
• neuter: αυτό

So:

• αυτός ο άνθρωπος
• αυτή η λέξη
• αυτό το σχόλιο

Greek agreement is much stricter than English here.

Το is the definite article: the.

In Greek, when you use a demonstrative like αυτό before a noun, you normally also use the article:

• αυτό το σχόλιο = this comment
• εκείνο το σπίτι = that house

So Greek usually says literally something like this the comment, not just this comment without the article.

Here it is a demonstrative adjective, because it modifies the noun σχόλιο.

• Αυτό το σχόλιο = this comment → adjective use
• Αυτό ήταν προσβολή. = This was an insult. → pronoun use

So in your sentence, αυτό is not standing alone; it is directly attached to το σχόλιο.

It is in the nominative case, because it is the subject of the verb ήταν.

The basic structure is:

• Αυτό το σχόλιο = subject
• ήταν = verb
• προσβολή = predicate noun

In sentences with to be, the subject is in the nominative, and the noun after the verb is also typically nominative in Modern Greek.

Ήταν is the imperfect / past form of είμαι (to be) for he/she/it and also they.

So:

• είναι = is / are
• ήταν = was / were

In your sentence, it means was, because the subject αυτό το σχόλιο is singular.

A useful thing to remember is that ήταν looks the same for singular and plural:

• Αυτό ήταν... = This was...
• Αυτά ήταν... = These were...

The rest of the sentence tells you whether it is singular or plural.

After είμαι / ήταν, Greek often leaves out the indefinite article when giving a classification or description.

So:

• Ήταν προσβολή. = It was an insult.
• Είναι γιατρός. = He/She is a doctor.

Adding μια is possible, but it changes the feel slightly:

• Ήταν προσβολή. = a neutral statement/classification
• Ήταν μια προσβολή. = it was an insult / kind of emphasizes it as one instance

So the version without μια is very natural.

Because it is being used as a predicate noun after ήταν.

In Greek, predicate nouns often appear without an article, especially when you are saying what something is rather than identifying a specific known item.

Compare:

• Αυτό ήταν προσβολή. = This was an insult.
• Αυτή ήταν η προσβολή που δεν ξέχασα. = That was the insult I never forgot.

In the first sentence, προσβολή is a category/description, not a specific previously identified insult.

Yes. In this sentence, προσβολή is in the nominative singular.

Even though English learners sometimes expect something like an object here, after to be Greek usually uses a predicate nominative, not an accusative.

So both parts are nominative:

• Αυτό το σχόλιο — nominative subject
• προσβολή — nominative predicate noun

That is the normal Greek pattern with demonstratives:

• αυτό το...
• αυτή η...
• αυτό το...
• εκείνος ο...
• εκείνη η...
• εκείνο το...

So the order is:

demonstrative + article + noun

Examples:

• αυτό το βιβλίο
• αυτή η πόρτα
• εκείνο το παιδί

This is just the standard structure you should memorize.

Yes. That is also grammatical.

Both are correct:

• Αυτό το σχόλιο ήταν προσβολή.
• Το σχόλιο αυτό ήταν προσβολή.

The second version can sound a bit more formal, emphatic, or stylistically marked depending on context. For most learners, αυτό το σχόλιο is the most straightforward and common pattern to learn first.

The difference is just past vs present:

• Αυτό το σχόλιο είναι προσβολή. = This comment is an insult.
• Αυτό το σχόλιο ήταν προσβολή. = This comment was an insult.

So if you are talking about something said in the past, ήταν is natural. If you are reacting to it now as a present statement, είναι may fit better.

A natural pronunciation is roughly:

af-TO to SKHO-lee-o EE-tan pros-vo-LEE

A more careful transliteration:

Aftó to schólio ítan prosvolí.

A few pronunciation notes:

• αυ before voiceless consonants often sounds like af → αυτό
• σχ sounds like skh / s+h depending on accent and speech
• the stress marks show which syllable gets emphasis:
  • αυτό
  • σχόλιο
  • ήταν
  • προσβολή

The accent mark shows which syllable is stressed.

In this sentence:

• αυτό → stress on the last syllable
• σχόλιο → stress on σχό
• ήταν → stress on the first syllable
• προσβολή → stress on the last syllable

Stress matters in Greek because it is part of the standard spelling and pronunciation. Learners should try to learn words together with their stress.

Yes, absolutely. It is grammatical and natural.

The difference is mostly one of style and nuance:

• ήταν προσβολή = more direct, categorical
• ήταν μια προσβολή = slightly more explicit as an insult

Both work. The version without μια is very common in Greek after forms of είμαι.

It is a completely normal Greek sentence. The structure is very natural:

• demonstrative phrase: αυτό το σχόλιο
• past of to be: ήταν
• predicate noun: προσβολή

So this is not awkward or overly literal. A native speaker would understand it immediately and find it natural.