Bitterness must be managed with inadequate legal organisation (7)
I believe the answer is:
rancour
'bitterness' is the definition.
(I know that bitterness can be written as rancour)
'managed with inadequate legal organisation' is the wordplay.
'managed' becomes 'ran' (I've seen this in another clue).
'with' is a charade indicator (letters next to each other).
'inadequate' means to remove the last letter (an incomplete or inadequate form of the word).
'legal organisation' becomes 'court' (law court).
'court' with its final letter taken away is 'cour'.
'ran'+'cour'='RANCOUR'
'must be' acts as a link.
(Other definitions for rancour that I've seen before include "Bitter feeling or ill will" , "Malicious hostility" , "Bitter resentment" , "Deep-seated enmity" , "'Bitterness, resentment (7)'" .)