Beim Pubquiz darf niemand bei der Stichfrage schummeln.

Beim is a contraction of bei dem.

• bei = at, during, in the context of
• dem = the dative form of der/das

So Beim Pubquiz literally means at the pub quiz or during the pub quiz.

In this sentence, it sets the situation: During the pub quiz ...

Because bei and in are used differently in German.

• bei often means at, during, or as part of an event/activity
• in usually means in(side) a physical space or sometimes in an abstract context

A Pubquiz is mainly understood as an event, so beim Pubquiz is the natural choice: at/during the pub quiz.

Using im Pubquiz would sound unusual in most contexts.

Because the preposition bei always takes the dative.

So:

• bei dem Pubquiz → beim Pubquiz

Also, Quiz is neuter in German: das Quiz.
That is why the article becomes dem in the dative.

Yes, you can absolutely say Niemand darf bei der Stichfrage schummeln.

German is a verb-second language in main clauses. That means the conjugated verb must come in the second position.

In your sentence:

• Beim Pubquiz = position 1
• darf = position 2
• niemand comes after that

So the sentence structure is correct because Beim Pubquiz has been placed first for emphasis or to set the scene.

Compare:

• Beim Pubquiz darf niemand bei der Stichfrage schummeln.
• Niemand darf beim Pubquiz bei der Stichfrage schummeln.

Both are grammatical, but the emphasis is slightly different.

Here darf means is allowed to / may.

Because the sentence has niemand, the meaning becomes:

• nobody is allowed to cheat

So this is about permission/prohibition, not ability.

Compare:

• Er darf gehen. = He may leave.
• Er kann gehen. = He is able to leave.

So darf here is about rules, not capability.

Because this sentence uses a modal verb: dürfen.

In German main clauses with a modal verb:

• the conjugated modal verb goes in position 2
• the main verb in the infinitive goes to the end

So:

• darf = conjugated modal verb
• schummeln = infinitive at the end

This is a very common pattern:

• Ich kann Deutsch sprechen.
• Du musst jetzt gehen.
• Wir dürfen hier nicht parken.

It means on the tie-break question or in the tie-breaker round/question.

Again, bei is being used in the sense of in connection with or during something.

So bei der Stichfrage schummeln means to cheat on the tie-break question.

Because bei takes the dative, and Stichfrage is feminine.

The noun is:

• die Stichfrage = the tie-break question

In the dative, feminine die becomes der:

• nominative: die Stichfrage
• dative: der Stichfrage

So:

• bei der Stichfrage

A Stichfrage is a question used to break a tie.

For example, if two teams have the same number of points in a pub quiz, there may be a Stichfrage to decide the winner.

So in this sentence, it refers to that special deciding question.

Schummeln means to cheat, especially in a relatively everyday context like:

• at school
• in a game
• in a quiz
• on a test

It often sounds a bit less formal than betrügen.

• schummeln = cheat, fudge, copy, sneak an unfair advantage
• betrügen = cheat, deceive, defraud

In a pub quiz, schummeln is the natural word.

Because the two bei phrases do different jobs:

• Beim Pubquiz = sets the general situation: at/during the pub quiz
• bei der Stichfrage = specifies the part of the quiz where cheating must not happen: on the tie-break question

So even though the same preposition appears twice, it is not wrong or unnatural.

You could translate it that way, but it sounds unnatural in English.

A more natural English version would be something like:

• During the pub quiz, nobody is allowed to cheat on the tie-break question.
• At the pub quiz, no one may cheat on the tie-breaker.

So the German structure is fine, but English would usually phrase it a bit differently.

Yes, it is used in German, especially in informal contexts. It is a borrowing from English.

You may also see variations such as:

• Pub-Quiz
• Kneipenquiz

All of these refer to the same basic idea: a quiz held in a pub or bar.

Normally, no. Niemand already means nobody/no one, so you usually do not add nicht.

Correct:

• Niemand darf schummeln.

Incorrect in standard usage:

• Niemand darf nicht schummeln.

That second version would create a double negative problem and change the meaning in a confusing way.

The sentence follows this pattern:

[time/place/context] + [conjugated verb] + [subject] + [other information] + [infinitive]

So here:

• Beim Pubquiz = context first
• darf = conjugated verb in second position
• niemand = subject
• bei der Stichfrage = additional phrase
• schummeln = infinitive at the end

This is a very typical German sentence pattern.