Supporter first to bring up insult (4)
I believe the answer is:
barb
'insult' is the definition.
(thesaurus)
'supporter first to bring up' is the wordplay.
'supporter' becomes 'bra' (I've seen this before**).
'first to' says to take the initial letters.
'up' says the letters should be written backwards (in down clue: letters go upwards).
The initial letter of 'bring' is 'b'.
'bra'+'b'='brab'
'brab' back-to-front is 'BARB'.
(Other definitions for barb that I've seen before include "added to wire?" , "Small prong on larger point" , "criticism" , "part of a habit" , "Aggressive remark directed at a person" .)