Judge's reports are full of resentment (7)
I believe the answer is:
arbiter
'judge's' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for arbiter that I've seen before include "Rear bit (anag.)" , "Referee or judge of rarebit" , "Someone with the power to settle the matter" , "Source of authority" , "One has the authority to settle disputes" .)