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' is a charade indicator (letters next to each other) (I've seen this in other clues).
'get out' becomes 'draw' (synonyms).
'a gun in retaliation' becomes 'back' (I can't explain this - if you can you should give a lot more credence to this answer).
'draw' put next to 'back' is 'DRAWBACK'.
'that's' acts as a 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" .)