Subterfuge could be so naive (7)
I believe the answer is:
evasion
'subterfuge' is the definition.
(I've seen this before)
'could be so naive' is the wordplay.
'could be' indicates anagramming the letters.
'so'+'naive'='sonaive'
'sonaive' is an anagram of 'EVASION'.
(Other definitions for evasion that I've seen before include "Circumvention" , "deception" , "Attempt to avoid the point of an argument" , "Act of avoiding" , "Avoidance; equivocation" .)