Soutěžící jsou na hospodském kvízu.

Soutěžící means contestant, competitor, or sometimes participant in a competition.

In this sentence, it is plural because of the verb jsou, which means are. So even though soutěžící can look the same in singular and plural, the verb tells you that here it means contestants.

This is very common in Czech: some words, especially ones ending in -ící, have the same form in more than one grammatical category, so you use the rest of the sentence to tell what is meant.

Here jsou is the present-tense plural form of být = to be.

• jsem = I am
• jsi/jseš = you are
• je = he/she/it is
• jsme = we are
• jste = you are
• jsou = they are

In normal Czech, you do not usually omit the present tense of to be in sentences like this. So:

• Soutěžící jsou na hospodském kvízu. = normal full sentence
• Soutěžící na hospodském kvízu. = incomplete in ordinary speech, unless it is a headline, note, or very elliptical style

Czech often uses na for being at an event, activity, or organized gathering.

So you commonly hear:

• na koncertě = at a concert
• na schůzce = at a meeting
• na večírku = at a party
• na kvízu = at a quiz

So na hospodském kvízu means at a pub quiz.

If you used v, it would sound less natural here, because v usually focuses more on being inside a place rather than attending an event.

Because after na, Czech uses different cases depending on the meaning:

• na + accusative = motion toward something
• na + locative = location, being at/on something

Here the sentence describes where the contestants are, not where they are going, so Czech uses the locative:

• na hospodském kvízu = at a pub quiz

That is why the adjective and noun change form:

• hospodský → hospodském
• kvíz → kvízu

Hospodský is an adjective related to hospoda, which means pub, inn, or tavern.

So:

• hospodský kvíz = pub quiz

It does not mean that the quiz belongs to a specific landlord or owner. It means the quiz is of the pub/tavern type, or connected with a pub setting.

Yes, there is a small difference.

• hospodský kvíz = pub quiz as a type of event
• kvíz v hospodě = a quiz in a pub

The second phrase only tells you the location. The first one sounds more like the established idea of a pub quiz. In many situations they can refer to the same real-world thing, but hospodský kvíz is the more natural set phrase for pub quiz.

Here soutěžící is in the nominative, because it is the subject of the sentence.

The basic structure is:

• Soutěžící = subject
• jsou = verb
• na hospodském kvízu = prepositional phrase saying where they are

So even though soutěžící can be tricky because its form does not change much, in this sentence its role is straightforward: it is the subject, so it is nominative.

Yes. Czech word order is fairly flexible, because case endings help show the grammatical roles.

The neutral order here is:

• Soutěžící jsou na hospodském kvízu.

But you could also say:

• Na hospodském kvízu jsou soutěžící.

That version puts more attention on where they are. It may sound like you are answering Where are the contestants?

So the meaning stays basically the same, but the emphasis changes.

A simple learner-friendly guide is:

• Soutěžící ≈ SOU-tye-zhee-tsee
• jsou ≈ zsoh or ysoh depending on how carefully you pronounce it
• na = nah
• hospodském ≈ HOS-pot-skehm
• kvízu ≈ KVEE-zoo

A few useful pronunciation points:

• Czech stress is usually on the first syllable of each word.
• ž sounds like the s in measure.
• í is a long ee sound.
• kvíz is a loanword, but it is pronounced in a Czech way.

No, kvíz is a borrowed word, ultimately from English quiz. But it is fully integrated into Czech and declines like a normal Czech noun:

• kvíz
• kvízu
• kvízem, etc.

So even though it comes from English, Czech treats it like an ordinary masculine noun.