Explosive leading article, surprisingly unorthodox (9)
I believe the answer is:
heretical
'unorthodox' is the definition.
(I've seen this before)
'explosive leading article surprisingly' is the wordplay.
'explosive' becomes 'he' (abbreviation for high explosive).
'leading' means one lot of letters go next to another.
'surprisingly' is an anagram indicator.
'article' with letters rearranged gives 'retical'.
'he'+'retical'='HERETICAL'
(Other definitions for heretical that I've seen before include "opposing the official line" , "preaching falsely" , "Unorthodox (in religion)" , "Dissenting" , "Contrary to popular belief" .)