Hit band pocketing millions (5)
I believe the answer is:
smash
'hit' is the definition.
(smash is a kind of hit)
'band pocketing millions' is the wordplay.
'band' becomes 'sash' (sash is a kind of band).
'pocketing' means one lot of letters goes inside another.
'millions' becomes 'm' (abbreviation).
'sash' going around 'm' is 'SMASH'.
(Other definitions for smash that I've seen before include "Shatter, break up" , "tremendous success!" , "- - and grab" , "Hard tennis shot" , "Violently break into pieces" .)