Magnify balls in front of art gallery (9)
I believe the answer is:
overstate
'magnify' is the definition.
(I know that magnify can be written as overstate)
'balls in front of art gallery' is the wordplay.
'balls' becomes 'overs' (an over is a sequence of balls bowled in cricket).
'in front of' is a charade indicator (letters next to each other) (some letters go in front of others).
'art gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'overs'+'tate'='OVERSTATE'
(Other definitions for overstate that I've seen before include "Exaggerate, go beyond bounds of truth" , "lay it on thick" , "Exaggerate, make too much of" .)