Couldn't stand trial when caught in the act (8)
I believe the answer is:
detested
'couldn't stand' is the definition.
(I've seen this in another clue)
'trial when caught in the act' is the wordplay.
'trial' becomes 'test' (synonyms).
'when caught in' is an insertion indicator.
'the act' becomes 'deed' (deed is a kind of act).
'test' put inside 'deed' is 'DETESTED'.
(Other definitions for detested that I've seen before include "Despised" , "Couldn't stand trial" , "Loathed over test deed" , "Cordially loathed" , "Greatly hated" .)