Wrong start, thus not starting (7)
I believe the answer is:
offence
'wrong' is the definition.
(thesaurus)
'start thus not starting' is the wordplay.
'start' becomes 'off' (as in 'from the off').
'thus' becomes 'hence' (synonyms).
'not starting' means to remove the first letter.
'hence' with its initial letter taken away is 'ence'.
'off'+'ence'='OFFENCE'
(Other definitions for offence that I've seen before include "An act punishable by law" , "Criminal action" , "Violation" , "An illegal act, cause of annoyance" , "The handler" .)