Perhaps Yellowstone employee top Republican axed might be upset? (5)

I believe the answer is:

anger

I'm a little stuck... Click here to teach me more about this clue!

'upset?' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe there's an association between them I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for anger that I've seen before include "Nettle" , "Wrath, ire" , "exasperation" , "Provoke annoyance" , "Range (anag)" .)

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