Itinerant worker chasing sin (6)
I believe the answer is:
errant
'itinerant' is the definition.
(thesaurus)
'worker chasing sin' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'chasing' means one lot of letters go next to another.
'sin' becomes 'err' (to sin is to err morally).
'ant' put after 'err' is 'ERRANT'.
(Other definitions for errant that I've seen before include "Quixotic" , "Nomadic" , "Travelling about or going astray" , "Offending" , "Wandering (as a knight?)" .)