Η προπονήτρια ξέρει ότι μια ήττα δεν αλλάζει όλο το πρωτάθλημα.

Η προπονήτρια means the (female) coach.

• η is the feminine singular definite article, meaning the
• προπονήτρια is a feminine noun meaning coach or trainer

Greek nouns have grammatical gender, and this noun is specifically feminine. If the coach were male, you would usually say ο προπονητής.

So:

• η προπονήτρια = the female coach
• ο προπονητής = the male coach

ξέρει is the 3rd person singular present tense of ξέρω, which means to know.

So:

• ξέρω = I know
• ξέρεις = you know
• ξέρει = he/she/it knows

Since the subject is η προπονήτρια (the coach), Greek uses ξέρει = she knows.

A useful note: ξέρω often means know in the sense of be aware of / know a fact. In this sentence, that fits perfectly: the coach knows that something is true.

ότι introduces a subordinate clause and means that.

So:

• Η προπονήτρια ξέρει ότι...
• The coach knows that...

It works very much like English that after verbs such as know, say, think, etc.

In everyday Greek, you may also see πως used in a similar way:

• ξέρει ότι...
• ξέρει πως...

Both can mean knows that... in this kind of sentence.

μια ήττα means a defeat.

• μια = a / one (feminine singular)
• ήττα = defeat, a feminine noun

Because ήττα is feminine, the indefinite article must also be feminine:

• ένας for masculine nouns
• μια / μία for feminine nouns
• ένα for neuter nouns

So μια ήττα is correct because both words are feminine singular.

Usually, they are just two written versions of the same word, both meaning a / one for feminine nouns.

In modern Greek:

• μια is very common in everyday writing
• μία may be used when someone wants to make the stress especially clear, or in slightly more careful writing

For most learners, you can treat them as the same word here.

δεν is the normal word for not before verbs in Greek.

So:

• αλλάζει = changes
• δεν αλλάζει = does not change

Greek normally places δεν directly before the verb it negates.

Examples:

• ξέρει = she knows

• δεν ξέρει = she does not know

• αλλάζει = it changes
• δεν αλλάζει = it does not change

αλλάζει is the 3rd person singular present tense of αλλάζω, meaning to change.

So here it means:

• (a defeat) does not change...

Why 3rd person singular? Because the subject of that clause is μια ήττα (a defeat), which is singular.

Basic pattern:

• αλλάζω = I change
• αλλάζεις = you change
• αλλάζει = he/she/it changes

This means the whole championship or the entire championship.

Breakdown:

• όλο = whole / entire
• το = the
• πρωτάθλημα = championship

The important grammar point is agreement. πρωτάθλημα is a neuter singular noun, so όλος must also appear in the neuter singular form:

• masculine: όλος
• feminine: όλη
• neuter: όλο

So:

• όλο το πρωτάθλημα = the whole championship

It is the direct object of αλλάζει, so yes, it is in the accusative case. But with many neuter singular nouns, the nominative and accusative forms are identical.

So even though πρωτάθλημα is the object, it looks the same as the dictionary form.

That is very common with neuter nouns in Greek.

For comparison:

• nominative: το πρωτάθλημα
• accusative: το πρωτάθλημα

Same form, different grammatical role.

Greek often does not use an explicit subject pronoun when the verb ending already shows the person and number.

In this clause, the subject is already expressed as μια ήττα (a defeat), so there is no need to add a separate word for it.

Greek generally avoids unnecessary subject pronouns unless there is emphasis or contrast.

So Greek prefers:

• μια ήττα δεν αλλάζει...

rather than something like:

• μια ήττα αυτή δεν αλλάζει...
  which would sound unnatural here

Yes. Greek word order is more flexible than English, although the version you have is very natural.

Standard order here is:

• Η προπονήτρια ξέρει ότι μια ήττα δεν αλλάζει όλο το πρωτάθλημα.

But Greek can move things around for emphasis. For example:

• Η προπονήτρια ξέρει ότι όλο το πρωτάθλημα δεν αλλάζει με μια ήττα would change the structure and feel, and is not the same sentence word-for-word, but it shows how Greek can reorganize ideas.

In your sentence, the order is straightforward and neutral:

1. subject: Η προπονήτρια
2. verb: ξέρει
3. clause introduced by ότι
4. subject of the clause: μια ήττα
5. negation + verb: δεν αλλάζει
6. object: όλο το πρωτάθλημα

So this is a very good sentence pattern to learn from.

A rough guide:

• Η προπονήτρια = ee pro-po-NEE-tria
• ξέρει = KSE-ri
• ότι = O-ti
• μια ήττα = mia EE-ta
• δεν αλλάζει = then a-LA-zi
• όλο το πρωτάθλημα = O-lo to pro-TA-thli-ma

A few useful pronunciation notes:

• ξ sounds like ks
• η, ι, υ, ει, οι are all pronounced like ee
• δ in modern Greek sounds like the th in this
• θ sounds like the th in think

Also, the written accent mark shows where the stress falls:

• προπονήτρια
• ξέρει
• ήττα
• αλλάζει
• πρωτάθλημα

Literally, πρωτάθλημα means championship, league competition, or title race, depending on context.

In sports talk, όλο το πρωτάθλημα can sound like:

• the whole championship
• the entire league campaign
• the whole title race

So even if the literal translation is championship, the natural English meaning can vary depending on the sport and context. The Greek itself is completely normal.