Craftsman's erratic if disturbed (9)
I believe the answer is:
artificer
'craftsman's' is the definition.
(synonyms)
'erratic if disturbed' is the wordplay.
'disturbed' is an anagram indicator (the order of letters is disturbed).
'erratic'+'if'='erraticif'
'erraticif' is an anagram of 'ARTIFICER'.
(Other definitions for artificer that I've seen before include "One into skill" , "Skilled craftsman" , "Skilled worker" , "Inventor who's skilful" , "Mechanic in the armed forces" .)