Set free, director is to attack (9)
I believe the answer is:
discharge
'set free' is the definition.
(thesaurus)
'director is to attack' is the wordplay.
'director' becomes 'd' (abbreviation eg in film reviews).
'to attack' becomes 'charge' (charging is a kind of attacking).
'd'+'is'+'charge'='DISCHARGE'
(Other definitions for discharge that I've seen before include "Put out" , "Send away - perform" , "Fire (a gun); release from custody" , "unload" , "empty" .)