Ninguém pode trapacear na partida.

Because ninguém is grammatically singular in Portuguese, even though it refers to no people.

So Portuguese uses:

• Ninguém pode... = No one can...
• not Ninguém podem...

This works like English nobody is rather than nobody are.

Because ninguém already makes the sentence negative.

In Portuguese, ninguém means no one / nobody, so you do not need não before the verb here.

• Ninguém pode trapacear na partida. = correct
• Ninguém não pode trapacear na partida. = generally not standard for this meaning

A useful pattern is:

• Ninguém sabe. = Nobody knows.
• Nada aconteceu. = Nothing happened.

When a negative word like ninguém is the subject, it already carries the negative meaning.

After poder (can / to be able to), the next verb stays in the infinitive.

So:

• pode trapacear = can cheat
• podem jogar = can play
• posso sair = I can leave

This is similar to English:

• can cheat
• not can cheats

So trapacear stays in its dictionary form, the infinitive.

Trapacear means to cheat, especially in a game, competition, or situation where someone breaks the rules unfairly.

It is a normal, understandable word in Brazilian Portuguese. Depending on context, Brazilians might also say:

• roubar = literally to steal, but in games it can mean to cheat / play unfairly
• fazer trapaça = to cheat / do something dishonest
• colar = to cheat, but usually in school/test contexts, not usually for a game

So for a match or game, trapacear fits well.

Because na is the contraction of:

• em + a = na

So:

• na partida = in the match / in the game

Portuguese very often contracts em with articles:

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

So em a partida is not the normal form; na partida is.

Yes, partida can mean different things depending on context.

Common meanings include:

• match / game
• departure

In this sentence, because of trapacear and the overall context, partida clearly means a game, match, or round of play.

For example:

• partida de futebol = soccer match
• partida de xadrez = chess game

So context tells you which meaning is intended.

Portuguese often uses definite articles more naturally than English does.

So na partida literally looks like in the match, but in English you may simply say in the game or sometimes just during play, depending on context.

Using the article here makes the phrase sound natural and specific:

• na partida = in the match / during the game

Without the article, em partida would usually not sound natural in this sentence.

Yes, often you can.

• Ninguém pode trapacear no jogo.
• Ninguém pode trapacear na partida.

Both can be correct, but there can be a slight nuance:

• jogo is the more general everyday word for game
• partida often sounds like a specific match, round, or contest

For example:

• jogo de cartas = card game
• partida de tênis = tennis match

In many contexts, either one works.

Yes. That is completely natural.

• Ninguém pode trapacear na partida.
• Na partida, ninguém pode trapacear.

The second version puts more emphasis on the match/game context.

Portuguese word order is somewhat flexible, especially when moving a prepositional phrase like na partida to the front.

It sounds neutral and correct. It is easy to understand and appropriate in standard Brazilian Portuguese.

Depending on the situation, a Brazilian speaker might also say things like:

• Ninguém pode roubar no jogo.
• Não pode trapacear na partida.
• É proibido trapacear na partida.

But your original sentence is perfectly natural, especially in rules, instructions, or general statements.

In Brazilian Portuguese, ninguém is pronounced approximately like neen-GHEN or neen-GAYN, depending on accent and how simplified the comparison is.

A few important points:

• The nh sounds like the ny in canyon
• The final m is usually not pronounced like a strong English m
• Instead, it helps nasalize the vowel before it

So the ending of ninguém has a nasal sound rather than a clear m sound.

No, ninguém itself already means no one / nobody, so it normally stands alone as a pronoun.

You would say:

• Ninguém chegou. = Nobody arrived.
• Ninguém pode trapacear. = No one can cheat.

You would not normally say something like ninguém pessoas or attach a plural noun after it.

If you want to say none of the players, Portuguese would usually use a different structure, such as:

• Nenhum dos jogadores pode trapacear.

That is a different pattern from ninguém.