Learn Hardcore Norwegian: Kvelden da hun ble sint, var det ingen som forstyrret henne. - The evening when she got angry, no one disturbed her.

Specific past: Kvelden da hun ble sint ... (that particular evening)
General/habitual: Når hun blir sint, ... (whenever she gets angry) Saying Kvelden når hun ble sint is not idiomatic.

Why is there a comma after "sint," and do I have to have it?

The comma separates the long, fronted time expression (Kvelden da hun ble sint) from the main clause. This is standard in written Norwegian. You do not put a comma inside the time phrase (no comma before da). Keep the comma after the fronted element; it also helps signal the upcoming inversion (var det).

Why is it "var det" and not "det var" after the comma?

Norwegian main clauses obey the V2 rule: the finite verb must be the second element. After fronting the time phrase, the verb comes next: Kvelden da hun ble sint, var det ... If you don’t front anything, you’d say Det var ....

What does "det" do in "var det ingen"? Why not "der"?

Here det is a dummy/expletive subject in an existential construction (Det var ...)—the Norwegian way to say “there was/were.” Der means the locational “there” and is not used for existential sentences.

Could I just say "Ingen forstyrret henne" instead?

Yes, that’s also correct, but the word order changes with fronting:

Fronted time, subject after verb: Den kvelden hun ble sint, forstyrret ingen henne.
Default order with time at the end: Ingen forstyrret henne den kvelden hun ble sint. The original Det var ingen som ... feels more like an “existential” statement (“there was no one who...”), while Ingen forstyrret ... directly negates the subject.

What is "som" doing in "ingen som forstyrret henne"? Can it be dropped?

Som introduces a relative clause and stands in for “who/that.” Here it’s the subject of the relative clause (som forstyrret ...), so it is required. You can drop som only when it is the object:

Subject: personen som kom (cannot drop som)
Object: personen (som) jeg møtte (optional)

Can "da" be omitted in "Kvelden da hun ble sint"?

Yes, you can also say Kvelden hun ble sint or Den kvelden hun ble sint. Using da often feels a bit clearer or slightly more formal, but all are idiomatic.

Why "ble sint" and not "var sint"?

Ble sint (past of bli) highlights the change of state (“got angry”). Var sint describes a state (“was angry”).

Kvelden da hun ble sint = the evening when she became angry.
Kvelden da hun var sint = the evening when she was (already) angry, suggesting a state throughout that time.

Why is it "henne" and not "hun"?

Henne is the object form (accusative) of hun. She is the subject in the first clause (hun ble sint), but the object of forstyrret in the second (forstyrret henne).

Can I replace "ingen" with "ikke noen"?

Yes. Det var ikke noen som forstyrret henne is acceptable and means the same. Ingen is shorter and a bit more neutral in writing; ikke noen can sound a touch more conversational or emphatic depending on context.

Is "forstyrret" the only correct past form?

In Bokmål both forstyrret and forstyrra are allowed. Forstyrret is more common in standard written Norwegian; forstyrra sounds more colloquial/dialectal.

Why is there no comma before "som forstyrret henne"?

Because it’s a restrictive relative clause (it defines which people we’re talking about—namely, none of those who disturbed her). Norwegian normally does not use a comma before som in restrictive relative clauses.

Can I move the time phrase to the end?

Yes, several placements are possible:

Det var ingen som forstyrret henne den kvelden hun ble sint.
Den kvelden hun ble sint, var det ingen som forstyrret henne.
Den kvelden hun ble sint, forstyrret ingen henne. Choice affects emphasis/information flow, not core meaning.

Why "Kvelden" with the definite ending, and do I need "den"?

Norwegian marks definiteness on the noun (kveld → kvelden). You can add the demonstrative for emphasis/contrast: Den kvelden (da) hun ble sint ... Both Kvelden da ... and Den kvelden da ... are correct; den adds a “that particular evening” feel.