Overwhelm unfashionable figure (9)
I believe the answer is:
outnumber
'overwhelm' is the definition.
'unfashionable figure' is the wordplay.
'unfashionable' becomes 'out' ('out' can be a synonym of 'unfashionable').
'figure' becomes 'number' (I've seen this before**).
'out'+'number'='OUTNUMBER'
(Other definitions for outnumber that I've seen before include "Be too many for in contest or conflict" , "Have more (eg troops) than" , "Be more numerous than" , "Exceed numerically" , "Exceed in figures" .)