Noun + に = Adverb?

[JesperHH]

急に describes とび込んだ
What confuses me is that it isn’t positioned behind the verb, but a noun うさぎ. How can it be an adverb but be positioned behind a noun and not a verb?

[rodan]

ウサギの is modifying the 穴, so it’s really just two に clauses after each other:
急に and ウサギの穴に

Thinking about it that way may make it clearer why 急に isn’t modifying ウサギ.

Note though that in general it might be best not get too hung up about what words specifically follow a particle like に - it’s not like の where it’s necessarily connected to the thing immediately after.

[LimeGreenTeknii]

I never thought that Japanese had a strict rule to always put the adverb before the verb. Even in English, adverbs don’t always have to come before the verb: “Unfortunately, my friends and I can’t come.”