Όταν τελειώσει το χρονόμετρο, τελειώνει ο γύρος και αποκλείεται ο παίκτης.

Because Greek often uses the aorist subjunctive after όταν when talking about a future event that will happen once before something else happens.

So:

• όταν τελειώσει το χρονόμετρο = when the timer runs out / when the timer finishes
• not just when the timer is finishing

Here, τελειώσει is from τελειώνω / τελειώνω and it refers to a single completed event.

A helpful way to think of it is:

• όταν + aorist subjunctive → when/once X happens
• όταν + present can be used more for repeated or ongoing situations, depending on context

In this sentence, the idea is: first the timer ends, then the round ends and the player is eliminated.

Because after certain words like όταν, Greek can use the subjunctive without writing να.

So although τελειώσει is a subjunctive form, όταν already introduces the kind of clause needed here:

• Όταν τελειώσει το χρονόμετρο...

You do not say:

• Όταν να τελειώσει... ✘

So the absence of να is completely normal.

This is a very common thing that confuses learners.

In the first part:

• Όταν τελειώσει το χρονόμετρο
  Greek uses the aorist subjunctive because this means when the timer has finished / when the timer runs out.

In the main part:

• τελειώνει ο γύρος
  Greek uses the present tense to describe what happens as a rule or as part of instructions/game mechanics.

So the sentence is not mixing tenses randomly. It is doing two different jobs:

1. τελειώσει = the trigger event
2. τελειώνει = the result that happens in that situation

English often does something similar:

• When the timer runs out, the round ends and the player is eliminated.

Here όταν means when.

In this sentence it introduces the condition or moment at which the next things happen:

• Όταν τελειώσει το χρονόμετρο... = When the timer runs out...

Depending on context, όταν can also have a repeated sense like whenever, but here it is best understood as when in a rule/instruction sense.

Χρονόμετρο means timer, stopwatch, or something that measures time.

In this sentence, το χρονόμετρο is best translated as the timer.

It is a neuter noun, which is why the article is το:

• το χρονόμετρο

Greek uses the definite article much more regularly than English does.

So:

• το χρονόμετρο = the timer
• ο γύρος = the round
• ο παίκτης = the player

In many cases, Greek sounds more natural with the article where English might sometimes omit it depending on style. In this sentence, the articles are completely expected because we are talking about specific things in the game situation.

Here γύρος means round.

So:

• τελειώνει ο γύρος = the round ends

Be careful, because γύρος can have other meanings in different contexts, such as:

• turn
• lap
• rotation
• even gyro in food-related contexts

But in a game sentence like this, round is the natural meaning.

Greek word order is more flexible than English word order.

So:

• τελειώνει ο γύρος
• ο γύρος τελειώνει

both mean the round ends.

Putting the verb first is very natural in Greek. It can make the sentence flow better or put focus on the action. Unlike English, Greek does not always need a strict subject + verb order.

Yes, αποκλείεται is a passive/middle form.

Here it means:

• the player is eliminated
• the player is excluded
• the player is disqualified

So:

• αποκλείεται ο παίκτης = the player is eliminated

This is natural Greek because the important point is what happens to the player, not who performs the action.

Yes. In other contexts, αποκλείεται can also mean things like:

• it is impossible
• it is ruled out
• it is excluded

For example:

• Αποκλείεται! = No way! / Impossible!

But in your sentence, because the subject is clearly ο παίκτης, the meaning is:

• the player is eliminated/disqualified

So context makes the meaning clear.

Yes.

Greek does not use θα after όταν in this kind of clause. Instead, it uses the subjunctive form:

• Όταν τελειώσει το χρονόμετρο...

That already gives the future sense: when the timer runs out.

In the main clause, Greek often uses the present tense for rules, instructions, or automatic outcomes:

• τελειώνει ο γύρος και αποκλείεται ο παίκτης

So the whole sentence clearly refers to what will happen in that game situation, even without θα.

Yes, very naturally.

It sounds like a rule in a game or activity:

• When the timer runs out, the round ends and the player is eliminated.

So even though the forms can refer to a future event, the whole sentence is best understood as describing what happens whenever this situation occurs in the game.

That is why the present tense in the main clause sounds especially natural.

It breaks down like this:

• Όταν τελειώσει το χρονόμετρο,
  When the timer runs out,

• τελειώνει ο γύρος
  the round ends

• και αποκλείεται ο παίκτης.
  and the player is eliminated.

So the structure is:

When X happens, Y happens and Z happens.

That is a very common Greek pattern.