Work on set is requiring effort after evidence of blow (9)
I believe the answer is:
dentistry
'work on set' is the definition.
(work on a set of teeth)
'is requiring effort after evidence of blow' is the wordplay.
'requiring' is a charade indicator (letters next to each other).
'effort' becomes 'try' (synonyms).
'after' says to put letters next to each other.
'evidence of blow' becomes 'dent' (indentation made by a smack or blow).
'is' put next to 'try' is 'istry'.
'istry' after 'dent' is 'DENTISTRY'.
(Other definitions for dentistry that I've seen before include "Medical discipline" , "It's trendy in profession of teeth-care" , "Practice relating to teeth" , "It's trendy to engage in care in teeth" , "Work which is looking down in the mouth?" .)