Trọng tài ở sân vận động.

Vietnamese often does not use a verb like to be in sentences about location.

So:

• Trọng tài ở sân vận động. = The referee is at the stadium.

Here, ở already expresses the idea of being in or at a place, so you do not need a separate word for is.

In this sentence, ở means at, in, or located at.

So:

• ở sân vận động = at the stadium

It is very commonly used for location:

• Tôi ở nhà. = I am at home.
• Cô ấy ở trường. = She is at school.

Depending on context, ở can sometimes also mean live at/in, but here it is just marking location.

By itself, trọng tài is a bare noun, so it does not automatically show:

• the referee
• a referee
• referees

Vietnamese often leaves this to context.

So Trọng tài ở sân vận động could mean:

• The referee is at the stadium
• A referee is at the stadium

If you want to be more specific, Vietnamese can add classifiers or quantity words, for example:

• Một trọng tài = a referee
• Các trọng tài = referees / the referees
• Vị trọng tài đó = that referee

Sân vận động means stadium.

Literally, you can think of it as something like:

• sân = yard, field, ground
• vận động = movement, physical activity, athletics

But as a fixed expression, sân vận động simply means stadium or sports stadium.

You should learn it as one vocabulary item.

Vietnamese often follows a straightforward pattern:

• Subject + location phrase

So here:

• Trọng tài = subject
• ở sân vận động = location

This gives:

• Trọng tài ở sân vận động.

This is similar to English The referee is at the stadium, except Vietnamese does not add is here.

Yes. That is natural.

• Trọng tài ở sân vận động. = The referee is at the stadium.
• Trọng tài đang ở sân vận động. = The referee is at the stadium right now / currently at the stadium.

Adding đang emphasizes that the situation is happening currently.

Without đang, the sentence is more neutral and can simply state the location as a fact.

In beginner explanations, ở is often taught as meaning at/in for location, but in actual Vietnamese grammar it can function in a verb-like way in sentences of location.

That is why:

• Tôi ở nhà.
• Anh ấy ở công ty.

are complete sentences, even without a separate word for is.

So for learners, the most useful idea is:

• treat ở as the key word that expresses being at/in a place

Usually, English chooses at or in based on the noun and context, but Vietnamese just uses ở for both.

Examples:

• ở nhà = at home
• ở trường = at school
• ở Việt Nam = in Vietnam
• ở sân vận động = at the stadium

So you do not need to memorize separate Vietnamese words for English at and in in basic location sentences like this one.

The tones are important:

• trọng has a nặng tone
• tài has a huyền tone

So the pitch pattern falls heavily on trọng, and tài has a lower falling tone.

A rough learner-friendly guide:

• trọng sounds somewhat like chawng with a heavy, cut-off tone
• tài sounds somewhat like tie with a falling tone

It is best to listen to native audio, because Vietnamese tones are hard to learn accurately from English spelling alone.

Yes, exactly.

A natural question would be:

• Trọng tài ở đâu? = Where is the referee?

And the answer:

• Trọng tài ở sân vận động. = The referee is at the stadium.

This is a very typical Vietnamese location pattern:

• [person/thing] + ở đâu?
• [person/thing] + ở + place

Yes, you can front the location for emphasis, though the basic sentence is simpler.

For example:

• Ở sân vận động, trọng tài đang chờ. = At the stadium, the referee is waiting.

But for the plain statement The referee is at the stadium, the most natural beginner form is still:

• Trọng tài ở sân vận động.

So fronting is possible, but not necessary here.

Not exactly.

• sân vận động = stadium
• sân bóng = ball field / football pitch / soccer field, depending on context

A sân vận động is usually a larger sports venue. A sân bóng usually refers more specifically to a playing field.

So in this sentence, sân vận động clearly means stadium, not just a field.