Disturb GI in a gallery (7)
I believe the answer is:
agitate
'disturb' is the definition.
(I know that disturb can be written as agitate)
'gi in a gallery' is the wordplay.
'in' is an insertion indicator.
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'a'+'tate'='atate'
'gi' inserted into 'atate' is 'AGITATE'.
(Other definitions for agitate that I've seen before include "Stir up (trouble?)" , "Stir; tie a tag (anag.)" , "Incite" , "Upset, stir" , "Trouble, make nervous" .)