Legal impediment lets Pope off (8)
I believe the answer is:
estoppel
'legal impediment' is the definition.
(I've seen this in another clue)
'lets pope off' is the wordplay.
'off' indicates an anagram.
'lets'+'pope'='letspope'
'letspope' is an anagram of 'ESTOPPEL'.
(Other definitions for estoppel that I've seen before include "Legal principle" , "bar" , "Conclusive admission" .)