Noun 勢い used as an adverb? > **** According to dictionaries, is a noun for momentum, force. In this sentence, isn't it used like an adverb to say that he knocked him on the ground with force?

This is indeed an uncommon adverbial usage of , but it means something different from what you are thinking:

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> Adverb
> 4\. naturally; necessarily

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> [

So what is the previous sentence? Does "naturally" make sense?

"Hit with force" would have been , , etc.