Australian soldier at the gallery causes stir (7)
I believe the answer is:
agitate
'stir' is the definition.
(I know that stir can be written as agitate)
'australian soldier at the gallery' is the wordplay.
'australian' becomes 'A' (common abbreviation).
'soldier' becomes 'GI' (GI can mean a US soldier).
'at' says to put letters next to each other.
'the gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'a'+'gi'+'tate'='AGITATE'
'causes' acts as a link.
(Other definitions for agitate that I've seen before include "Upset, stir" , "Disturb or shake" , "Campaign" , "Perturb" , "Stir; arouse" .)