كلما انتهى الشوط، خرج المشجعون من مقاعدهم.

كلما means whenever or every time that. It introduces a repeated relationship between two actions.

So the structure is:

• كلما انتهى الشوط = whenever the half/period ended
• خرج المشجعون من مقاعدهم = the fans got out of their seats

The important idea is repetition. This is not just when once; it means the same thing happened each time.

Arabic commonly uses the past tense after كلما to describe repeated events in a narrative or general past situation.

Here:

• انتهى = ended
• خرج = went out / got up

Even though the meaning is repeated, Arabic still uses the past because each individual event is seen as completed: the half ended, then the fans got up. English often does something similar in storytelling: Whenever the period ended, the fans got out of their seats.

So the past tense here does not mean it happened only once.

This is a very common feature of Standard Arabic word order.

In a normal verb-subject sentence, the verb is often singular, even if the subject that follows is plural:

• خرج المشجعون = literally went out the fans
• natural English: the fans went out

Because the subject comes after the verb, the verb stays singular masculine here: خرج.

If you put the subject first, then full agreement is used:

• المشجعون خرجوا من مقاعدهم

Both can be correct, but the sentence you were given uses the common verbal pattern.

Because المشجعون is a sound masculine plural in the nominative case.

Breakdown:

• singular: مشجع = fan, supporter
• plural: مشجعون = fans/supporters

It ends in -ون because it is the subject of the verb, and subjects are nominative.

If it were accusative or genitive, you would usually see -ين instead:

• رأيت المشجعين = I saw the fans
• مررت بالمشجعين = I passed by the fans

So in this sentence, المشجعون is nominative because it is the doer of خرج.

انتهى is the past tense, third person masculine singular, meaning ended or came to an end.

It matches الشوط, which is masculine singular, so:

• انتهى الشوط = the half/period ended

This verb is also a weak verb ending in ى. Its basic dictionary form is انتهى - ينتهي.

So a learner may notice that it does not look like a regular past-tense form such as خرج. That is because the last root letter is weak, which affects its shape.

Because الشوط is grammatically masculine, not feminine.

So the correct agreement is:

• انتهى الشوط = masculine singular
• انتهت would be used with a feminine singular noun

For example:

• انتهت المباراة = the match ended

So the form of the verb depends on the gender and number of the subject.

Literally, it means from their seats.

Breakdown:

• من = from
• مقاعد = seats
• هم = their

So:

• مقاعدهم = their seats

In English, the most natural translation may be out of their seats or up from their seats, depending on context. But the Arabic wording is literally from their seats.

هم is an attached pronoun meaning their or them, depending on context.

Here it shows possession:

• مقاعد = seats
• مقاعدهم = their seats

This pronoun refers back to المشجعون.

So Arabic often expresses possession by attaching a pronoun directly to the noun, instead of using a separate word like of.

This is an excellent comparison.

• كلما = whenever / every time
• عندما = when

The difference is that كلما strongly suggests repetition.

So:

• كلما انتهى الشوط، خرج المشجعون من مقاعدهم
  = Whenever the half ended, the fans got out of their seats

This means it happened repeatedly.

But:

• عندما انتهى الشوط، خرج المشجعون من مقاعدهم
  = When the half ended, the fans got out of their seats

This could describe one specific occasion.

The comma is helpful, but it is not the core grammatical issue.

It separates the introductory clause:

• كلما انتهى الشوط،
  from the main clause:
• خرج المشجعون من مقاعدهم

In modern written Arabic, this punctuation is very normal and makes the sentence easier to read. But the sentence would still be understandable without it, especially in unvocalized everyday writing.

So it is best to think of the comma here as standard and useful, not as something that creates the grammar itself.