Imperfect article on Jack — twisted etc (6)
I believe the answer is:
reject
'imperfect article' is the definition.
(reject can mean an imperfect article or thing)
'on jack twisted etc' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'jack' becomes 'J' (playing card abbreviation).
'twisted' indicates anagramming the letters.
'etc' is an anagram of 'ect'.
're'+'j'+'ect'='REJECT'
(Other definitions for reject that I've seen before include "Refuse to consider (something)" , "Dismiss (as faulty)" , "substandard article" , "Throw out" , "Refuse to accept, repulse" .)