Hates trials supporting defence's case (7)
I believe the answer is:
detests
'hates' is the definition.
('detest' can be a synonym of 'hate')
'trials supporting defence's case' is the wordplay.
'trials' becomes 'tests' ('test' can be a synonym of 'trial').
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'case' means to remove the middle letters.
'defence' with its middle taken out is 'de'.
'tests' after 'de' is 'DETESTS'.
(Other definitions for detests that I've seen before include "Abominates" , "Abhors" , "Cordially loathe" , "Loathes" , "Hates" .)