Lack support to carry gun around (8)
I believe the answer is:
shortage
'lack' is the definition.
(shortage is a kind of lack)
'support to carry gun around' is the wordplay.
'support' becomes 'shore' (I've seen this before**).
'to carry' means one lot of letters goes inside another.
'gun' becomes 'gat' (gat is a kind of gun).
'around' says the letters should be written in reverse.
'gat' backwards is 'tag'.
'shore' enclosing 'tag' is 'SHORTAGE'.
(Other definitions for shortage that I've seen before include "Need" , "Dearth, lack" , "Deficit" , "Insufficiency" , "Want" .)