Club servant becomes superhero (6)
I believe the answer is:
batman
'superhero' is the definition.
(DC superhero)
'club servant' is the wordplay.
'club' becomes 'bat' (as in sporting equipment).
'servant' becomes 'man' (man is a kind of servant).
'bat'+'man'='BATMAN'
'becomes' acts as a link.
(Other definitions for batman that I've seen before include "champion for justice" , "Bantam assuming role of masked crusader" , "Masked crusader of cartoon and film" , "'British military orderly, with Robin as a sidekick? (6)'" , "He helps the officer" .)