A pact goes wrong — he’s blamed unfairly (9)
I believe the answer is:
scapegoat
'he's blamed unfairly' is the definition.
(a scapegoat is unfairly blamed for something)
'a pact goes wrong' is the wordplay.
'wrong' indicates anagramming the letters.
'a'+'pact'+'goes'='apactgoes'
'apactgoes' is an anagram of 'SCAPEGOAT'.
(Other definitions for scapegoat that I've seen before include "One blamed for others' mistakes" , "One given the blame" , "One who takes the blame for others" , "Patsy" , "Fall guy" .)