Snag not initially an irritation (4)
I believe the answer is:
itch
'an irritation' is the definition.
(I've seen this in another clue)
'snag not initially' is the wordplay.
'snag' becomes 'hitch' (synonyms).
'not initially' means to remove the first letter.
'hitch' with its initial letter taken off is 'ITCH'.
(Other definitions for itch that I've seen before include "Restless longing" , "Uncomfortable feeling" , "Contagious skin infection" , "cause irritation" , "Something that needs a scratch" .)