Fighter at amateur boxing won judicial decision (5)
I believe the answer is:
fatwa
'judicial decision' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?
'fighter at amateur boxing won' is the wordplay.
'fighter' becomes 'F' (abbreviation in war plane e.g. F-w6 etc.).
'amateur' becomes 'a'.
'boxing' is an insertion indicator ('box' can mean contain, as in to put in a box).
'won' becomes 'w' (I've seen this in other clues).
'at'+'a'='ata'
'ata' enclosing 'w' is 'atwa'.
'f'+'atwa'='FATWA'
Can you help me to learn more?
(Other definitions for fatwa that I've seen before include "Legal ruling by Islamic leader, as against Salman Rushdie" , "Islamic opinion" , "Muslim decree or formal legal judgement" , "Legal ruling by Islamic religious leader" , "Muslim ruling" .)