Hero outlaw guarding cash machine (6)
I believe the answer is:
batman
'hero' is the definition.
(I know that Batman has the occupation superhero)
'outlaw guarding cash machine' is the wordplay.
'outlaw' becomes 'ban' (banning is a kind of outlawing).
'guarding' is an insertion indicator.
'cash machine' becomes 'a t m' (synonyms).
'ban' going around 'atm' is 'BATMAN'.
(Other definitions for batman that I've seen before include "who'd fight crime?" , "gives help to one in a mess?" , "'British military orderly, with Robin as a sidekick? (6)'" , "British military orderly and comic book hero" , "Comic/film superhero" .)