Kalau bola itu kena jendela, Ayah pasti marah.

Yes. In this sentence, kalau means if and introduces the condition:

• Kalau bola itu kena jendela = If the ball hits the window

Kalau is very common in everyday Indonesian. It is slightly more conversational than jika, which also means if but can sound a bit more formal or written.

So:

• Kalau bola itu kena jendela, Ayah pasti marah.
• Jika bola itu kena jendela, Ayah pasti marah.

Both are correct, but kalau is the more natural everyday choice.

In Indonesian, itu often comes after the noun when it means that/the in a specific sense.

So:

• bola itu = that ball / the ball

This is normal noun order in Indonesian:

• rumah itu = that house
• anak itu = that child
• jendela itu = that window

By contrast, itu can come before something in other structures, but for a simple noun phrase like this, bola itu is the expected pattern.

Here, kena means something like to hit, to be struck by, or to come into contact with.

So bola itu kena jendela literally feels closer to:

• the ball comes into contact with the window
• the ball hits the window
• the window gets hit by the ball

A useful thing to know is that kena often focuses on something being affected by contact. In other contexts, it can also mean things like:

• kena hujan = get rained on
• kena pukul = get hit
• kena masalah = run into trouble
• kena denda = get fined

So it is a very flexible everyday word.

Because Indonesian often does not need a preposition where English does.

In English, we might say:

• hit the window
• hit against the window
• strike the window

In Indonesian, kena jendela is already enough. The object directly follows:

• bola itu kena jendela

This is normal Indonesian structure. You do not need an extra preposition here.

Yes, other words are possible, but they sound a bit different.

• kena = very common, natural, everyday, broad meaning of hit/contact
• mengenai = more formal, often used in writing or careful speech
• menabrak = crash into / collide with, usually stronger

So:

• Kalau bola itu kena jendela...
  Very natural in everyday speech.

• Kalau bola itu mengenai jendela...
  Correct, but more formal.

• Kalau bola itu menabrak jendela...
  Possible, but sounds stronger, like an impact or collision.

For a simple everyday warning, kena is probably the most natural choice.

Because Indonesian often does not mark future time as explicitly as English does.

In English, we usually say:

• Dad will definitely be angry

In Indonesian, context is often enough. Since the first clause is a condition introduced by kalau, the second clause is naturally understood as the result in the future:

• Ayah pasti marah = Dad will definitely be angry

The word pasti already helps give the sense of a predictable result.

You could add akan for future:

• Ayah pasti akan marah

This is also correct, but in many everyday sentences, it is not necessary.

Pasti means definitely, certainly, or for sure.

In this sentence:

• Ayah pasti marah = Dad will definitely be angry

It comes before marah and modifies the whole statement.

This is a very common placement:

• Dia pasti datang. = He will definitely come.
• Mereka pasti tahu. = They definitely know.

You may sometimes hear slight variations in placement for emphasis, but subject + pasti + predicate is a very common and safe pattern.

It is often best understood as an adjective/state word meaning angry.

So:

• Ayah marah = Dad is angry
• Ayah pasti marah = Dad will definitely be angry

Indonesian does not need a verb meaning to be in sentences like this. That is why there is no separate word for is.

Compare:

• Ayah marah = Dad is angry
• Jendela itu besar = The window is big
• Bola itu merah = The ball is red

So marah behaves like a predicate without needing is.

Because here Ayah is being used like a name or title for a specific person: Dad.

Indonesian commonly capitalizes family terms when they are used as a form of address or as a name-like reference:

• Ayah = Dad
• Ibu = Mom / Mrs. / Mother
• Kakak = older sibling
• Paman = Uncle

But if the word is used more generally, it may be lowercase:

• Ayah saya marah. = My father is angry.
• Seorang ayah harus sabar. = A father should be patient.

In your sentence, capital Ayah shows it means Dad as a specific person.

Because Indonesian usually leaves out the equivalent of to be in simple statements.

English needs:

• Dad is angry

Indonesian normally just says:

• Ayah marah

Likewise:

• Bola itu besar = The ball is big
• Jendela itu kotor = The window is dirty
• Dia guru = He/She is a teacher

This is one of the most important differences from English. In many basic sentences, no linking verb is needed.

The sentence follows this pattern:

• Kalau + condition, result

So:

• Kalau bola itu kena jendela = If the ball hits the window
• Ayah pasti marah = Dad will definitely be angry

This structure is extremely common in Indonesian.

More examples:

• Kalau hujan, kami tidak pergi.
  If it rains, we won’t go.

• Kalau kamu belajar, kamu pasti lulus.
  If you study, you will definitely pass.

The comma is also normal when the kalau clause comes first.

Yes. Indonesian can also put the main clause first.

So you can say:

• Kalau bola itu kena jendela, Ayah pasti marah.
• Ayah pasti marah kalau bola itu kena jendela.

Both are correct.

When the kalau clause comes first, a comma is commonly written. When it comes second, a comma is often not used.

It can mean either, depending on context.

• bola itu literally looks like that ball
• but in real usage it can also work like the ball, meaning a specific ball both speakers know about

This is very common in Indonesian. Itu often helps mark something as specific or already identifiable, not just physically distant.

So in a sentence like this, a translation could be:

• If that ball hits the window...
• If the ball hits the window...

Both are possible depending on the situation.

Yes. If you want a stronger warning tone, Indonesian often uses expressions like kalau sampai.

For example:

• Kalau bola itu kena jendela, Ayah pasti marah.
  If the ball hits the window, Dad will definitely be angry.

• Kalau sampai bola itu kena jendela, Ayah pasti marah.
  If the ball ends up hitting the window, Dad will definitely be angry.

Kalau sampai adds a sense of if it actually happens / if it comes to that, which can sound more cautionary or dramatic.

The original sentence is already natural, though, and is simpler for learners.