Pig-headed operative is supporter of faction (8)
I believe the answer is:
partisan
'supporter of faction' is the definition.
'partisan' can be an answer for 'supporter' (partisan is a kind of supporter). I'm not certain of the 'of faction' bit.
'pig-headed operative is' is the wordplay.
I cannot really see how this works, but
'is' is present in the answer.
'pig-headed' could be 'p' (start (head) of the word pig) and 'p' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for partisan that I've seen before include "Happening immediately" , "champion" , "Prejudiced towards one side" , "In Sparta (anag)" , "Prejudiced towards one cause" .)