Rejection in deal going wrong (6)
I believe the answer is:
denial
'rejection' is the definition.
(rejection of a claim)
'in deal going wrong' is the wordplay.
'going wrong' indicates anagramming the letters.
'in'+'deal'='indeal'
'indeal' anagrammed gives 'DENIAL'.
(Other definitions for denial that I've seen before include "Rejection of a request" , "Renunciation" , "Refusal to believe an unacceptable truth" , "Refusal to accept an unpalatable truth" , "Daniel (anag.)" .)