Drawback; sharp projection (4)
I believe the answer is:
snag
This clue is a double definition.
'drawback' is the first definition.
(I've seen this before)
'sharp projection' is the second definition.
(I've seen this in another clue)
(Other definitions for snag that I've seen before include "Sharp protuberance; catch" , "Minor difficulty" , "Minor hitch" , "Catch - disadvantage" , "Difficulty; catch" .)