Learn Hardcore Norwegian: De må avlyse kampen i kveld. - They must cancel the match tonight.

In modern Norwegian, the formal you (De/Dem) is very rarely used, and mostly in very formal letters.
At the beginning of a sentence, De is capitalized anyway, so you have to use context.
In normal, everyday language, when you see De as the subject of a sentence like this, you should read it as they.

What exactly does må mean, and how is it different from måtte?

Må is a modal verb meaning must / have to in the present tense.

De må avlyse … = They have to / must cancel … (now or in the near future).
De måtte avlyse … = They had to cancel … (past tense).

So:

må = present
måtte = past

There is also a past participle måttet, but it is rarely used and you can basically ignore it at beginner/intermediate level.

Why is avlyse in the infinitive without å after må?

In Norwegian, modal verbs are followed by the bare infinitive, i.e. the infinitive without å.

Common pattern:

må
- infinitive: må avlyse
kan
- infinitive: kan spille (can play)
vil
- infinitive: vil dra (wants to / will go)

You would say:

De må avlyse kampen. ✅
Not: De må å avlyse kampen. ❌

What is the nuance of må avlyse compared with just avlyser?

De avlyser kampen i kveld. = They are cancelling the match tonight. (A neutral statement about what is happening.)
De må avlyse kampen i kveld. = They have to cancel the match tonight. (There is a necessity, obligation, or no other choice.)

So må adds the idea of obligation/necessity.

Why is it kampen and not kamp?

Norwegian usually marks definiteness by adding an ending to the noun instead of using a separate word like the.

For kamp (a match / a game / a fight), the forms are:

en kamp – a match
kampen – the match
kamper – matches (indefinite plural)
kampene – the matches (definite plural)

So kampen means the match. The sentence talks about a specific, known match, so the definite form is used.

What gender is kamp, and does that affect kampen?

Kamp is grammatically masculine.

Masculine nouns in Bokmål usually form the definite singular with -en:

en kamp → kampen
en bil → bilen
en stol → stolen

So kampen follows the regular masculine pattern.

Could kamp here also mean a fight or battle?

Yes. Kamp is a general word meaning:

a sports match / game
a fight / battle / struggle

The exact meaning depends on context. With avlyse kampen i kveld most learners (and native speakers) would first think of a sports match being cancelled, but it could theoretically be another type of kamp.

Why is it i kveld and not something like på kvelden or om kvelden?

These expressions have different meanings:

i kveld = this evening / tonight (a specific, upcoming evening)
på kvelden / om kvelden(e) = in the evenings (habitual, in general)

So:

De må avlyse kampen i kveld.
They have to cancel the match this evening (tonight).
De trener alltid på kvelden.
They always train in the evenings (as a routine).

Can i kveld go somewhere else in the sentence?

Yes. Word order is fairly flexible, but the neutral, most common order is the one you have:

De må avlyse kampen i kveld. (neutral)

You can move i kveld for emphasis:

I kveld må de avlyse kampen. (emphasis on tonight, e.g. not tomorrow)
De må i kveld avlyse kampen. (possible, but sounds a bit more formal/written or marked)

All are grammatically correct; the difference is mostly in emphasis and style.

How would I turn this into a yes/no question: Do they have to cancel the match tonight?

For yes/no questions in Norwegian, you normally put the verb first:

Må de avlyse kampen i kveld?
= Do they have to cancel the match tonight?

Structure:

Statement: De må avlyse kampen i kveld.
Question: Må de avlyse kampen i kveld?

Norwegian uses the present tense må here, but in English we say have to cancel tonight. Is that normal?

Yes. Norwegian very often uses the present tense to talk about the near future, especially with time expressions like i kveld, i morgen, snart.

Examples:

Jeg drar til Oslo i morgen. = I’m going to Oslo tomorrow.
Vi spiser senere. = We’ll eat later.
De må avlyse kampen i kveld. = They have to cancel the match tonight.

So the present tense in Norwegian can easily refer to future time when the context makes it clear.

How do you pronounce må, avlyse, and kampen?

Approximate pronunciation (standard East Norwegian):

må – like mo in more, with a long å sound: [moː]
avlyse – [ˈɑːvˌlyːsə]
- av – like ahv (with a long a-sound)
- ly – like lee with rounded lips (the y sound)
- se – like suh (schwa at the end)
kampen – [ˈkɑmpən]
- All consonants are pronounced; p is not silent.
- Final -en is a weak syllable [ən].

In fast speech, kampen may sound more like [ˈkɑmpn] or [ˈkɑm.pən], but every letter is basically there.