Crossword Genius

Hierarchy protecting Liberal, getting one’s back up (8)

Ross

I believe the answer is:

rankling

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

'hierarchy protecting' is the definition.
Although both the answer and definition are present participle verbs, I can't understand how they can define each other.

'liberal getting one's back up' is the wordplay.
I cannot really understand how this works, but
'liberal' could be 'l' (abbreviation) and 'l' is found within the answer.
'one' could be 'an' (an apple is one apple) and 'an' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for rankling that I've seen before include "causing some bitterness" , "Causing endless annoyance" , "causing resentment" , "leaving a nasty taste in one's mouth" , "annoying" .)

I've seen this clue in The Times.
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