Opposed to disturbing a nit (4)
I believe the answer is:
anti
'opposed to' is the definition.
(I've seen this before)
'disturbing a nit' is the wordplay.
'disturbing' indicates anagramming the letters (I've seen this in other clues).
'a'+'nit'='anit'
'anit' with letters rearranged gives 'ANTI'.
(Other definitions for anti that I've seen before include "Prefix meaning against" , "Prefix meaniing against" , "not favoured" , "(Person who is) not in favour" , "Adversary" .)