Will get out a gun in retaliation - that's the snag (8)
I believe the answer is:
drawback
'the snag' is the definition.
(I've seen this before)
'will get out a gun in retaliation' is the wordplay.
'will' means one lot of letters go next to another (I've seen this in other clues).
'get out' becomes 'draw' (synonyms).
'a gun in retaliation' becomes 'back' (I can't justify this - if you can you should believe this answer much more).
'draw'+'back' is 'DRAWBACK'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for drawback that I've seen before include "Limitation, disadvantage" , "Catch" , "Snag" , "Disadvantage, problem" , "Hindrance - disadvantage" .)