Rebel’s hip and knees ultimately needing speedy action? (9)
I believe the answer is:
insurgent
'rebel's' is the definition.
(synonyms)
'hip and knees ultimately needing speedy action?' is the wordplay.
'hip' becomes 'in' (both can mean fashionable).
'and' says to put letters next to each other.
'ultimately' says to take the final letters.
'needing' means one lot of letters go next to another.
'speedy action?' becomes 'urgent' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The final letter of 'knees' is 's'.
'in'+'s'+'urgent'='INSURGENT'
Can you help me to learn more?
(Other definitions for insurgent that I've seen before include "Unresting like a rebel" , "Rebel, revolutionary" , "freedom fighter" , "rising" , "Revolting" .)