Unusually deft clue I penned? Sneaky! (9)
I believe the answer is:
deceitful
'sneaky' is the definition.
(thesaurus)
'unusually deft clue i penned?' is the wordplay.
'unusually' is an anagram indicator.
'penned?' is an insertion indicator (inserted letters are enclosed or penned in).
'deft'+'clue'='deftclue'
'deftclue' anagrammed gives 'decetful'.
'decetful' enclosing 'i' is 'DECEITFUL'.
(Other definitions for deceitful that I've seen before include "cheating" , "Duplicitous" , "Sly" , "Deliberately misleading" , "unreliable" .)