Disturb American soldier in a gallery (7)
I believe the answer is:
agitate
'disturb' is the definition.
(I know that disturb can be written as agitate)
'american soldier in a gallery' is the wordplay.
'american soldier' becomes 'GI' (informal term for a US soldier).
'in' means one lot of letters goes inside another.
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'a'+'tate'='atate'
'gi' put within 'atate' is 'AGITATE'.
(Other definitions for agitate that I've seen before include "Stir; tie a tag (anag.)" , "Disturb or shake" , "Disturb or stir up" , "Stir vigorously" , "Disturb, cause to worry" .)