Being sarcastic, Clancy's badly out of line! (7)
I believe the answer is:
cynical
'being sarcastic' is the definition.
(thesaurus)
'clancy's badly out of line' is the wordplay.
'badly' is an anagram indicator (letters in the wrong order).
'out' means one lot of letters goes inside another.
'of line' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'clancy' with letters rearranged gives 'cyncal'.
'cyncal' enclosing 'i' is 'CYNICAL'.
Can you help me to learn more?
(Other definitions for cynical that I've seen before include "Adjective for person who never believes in good motives" , "Sceptical, mocking" , "unsentimental?" , "streetwise" , "Believing the worst of motives" .)