Demanding army officer must interrupt leave (7)
I believe the answer is:
exigent
'demanding army' is the definition.
'exigent' can be an answer for 'demanding' (thesaurus). I'm not sure about the 'army' bit.
'officer must interrupt leave' is the wordplay.
'officer' becomes 'gen' (abbreviation for general).
'must interrupt' is an insertion indicator.
'leave' becomes 'exit' ('exit' can be a synonym of 'leave').
'gen' put into 'exit' is 'EXIGENT'.
Can you help me to learn more?
(Other definitions for exigent that I've seen before include "Exacting, requiring much" , "Urgent and taxing" , "Pressing and urgent" , "Urgent and exacting" , "Pressing; demanding" .)