Refusal to be nailed, possibly (6)
I believe the answer is:
denial
'refusal' is the definition.
(I've seen this in another clue)
'nailed possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'nailed' is an anagram of 'DENIAL'.
'to be' acts as a link.
(Other definitions for denial that I've seen before include "Negation" , "Act of asserting that something alleged is not true" , "Refusal to admit painful truths" , "Rejection or refusal" , "Renunciation" .)