It's wrong to disturb inert croc (9)
I believe the answer is:
incorrect
'it's wrong' is the definition.
(synonyms)
'to disturb inert croc' is the wordplay.
'to disturb' indicates anagramming the letters (I've seen 'disturbed' mean this (the order of letters is disturbed)).
'inert'+'croc'='inertcroc'
'inertcroc' is an anagram of 'INCORRECT'.
(Other definitions for incorrect that I've seen before include "Erroneous" , "False, wrong" , "Place of refuge" , "Not accurate" .)