Ο διαιτητής σφυρίζει στο τέλος του παιχνιδιού.

Ο is the masculine singular definite article, so here it means the.

Greek uses the definite article very often with specific nouns, including professions and roles. So ο διαιτητής is the normal way to say the referee.

Without the article, διαιτητής would usually sound more like:

• a dictionary form
• a more general label
• or part of a different structure, not this simple subject phrase

So in this sentence, ο διαιτητής is just the natural way to say the referee.

Διαιτητής is in the nominative singular, because it is the subject of the sentence: the referee is the one doing the action.

The ending -ής is just part of this noun’s normal masculine form. Many Greek masculine nouns follow this pattern.

A few forms are:

• ο διαιτητής = the referee
• του διαιτητή = of the referee
• τον διαιτητή = the referee (object)

So here ο διαιτητής is nominative because it is the subject of σφυρίζει.

Σφυρίζει is the 3rd person singular present form of σφυρίζω.

Literally, it means whistles. In a sports context, it often means:

• blows the whistle
• signals with the whistle
• sometimes more broadly, calls or ends play

So the basic idea is that the referee performs the whistle action.

A quick present-tense pattern:

• σφυρίζω = I whistle
• σφυρίζεις = you whistle
• σφυρίζει = he/she/it whistles

Greek present tense can be used for a general, habitual, or standard action, just like English present tense.

So this sentence most naturally sounds like:

• something that generally happens
• a typical action in that situation
• or a simple present description

It does not have to mean that the action is happening right now.

If you wanted a completed past action, Greek would use a different form, for example:

• σφύριξε = he/she whistled

Στο is the contracted form of σε + το.

So:

• σε το becomes στο

This contraction is normal and standard in Greek.

The preposition σε can mean:

• in
• on
• at
• to

Here, in στο τέλος, it means at the end.

Τέλος is a neuter noun meaning end.

In the phrase στο τέλος, the preposition σε takes the accusative case. But for many neuter nouns, the nominative and accusative look the same, so the word stays τέλος.

So:

• το τέλος = the end
• στο τέλος = at the end

This is a very common expression in Greek.

Because after τέλος, Greek normally uses the genitive to mean of something.

So:

• το τέλος του παιχνιδιού = the end of the game

Here:

• του is the genitive article
• παιχνιδιού is the genitive singular of παιχνίδι

Base form:

• το παιχνίδι = the game

Genitive form:

• του παιχνιδιού = of the game

This is one of the most useful Greek patterns to learn:

• το τέλος του μαθήματος = the end of the lesson
• το τέλος της ταινίας = the end of the film

This is a normal stress change in Greek.

The basic form is:

• παιχνίδι

But the genitive singular is:

• παιχνιδιού

Many neuter nouns ending in -ι behave like this, especially in forms ending in -ιού.

Another common example:

• το σπίτι = the house
• του σπιτιού = of the house

So the change is not random; it is part of the noun’s normal inflection pattern.

Yes. Greek word order is more flexible than English word order because the endings and articles already show the grammatical relationships.

The original sentence:

• Ο διαιτητής σφυρίζει στο τέλος του παιχνιδιού.

This is a neutral, straightforward order.

But Greek could also say:

• Στο τέλος του παιχνιδιού σφυρίζει ο διαιτητής.

That would shift the emphasis, for example toward when the action happens.

So the original order is the most neutral one, but other orders are possible depending on style or emphasis.