A bishop caught in the sack is excluded (6)
I believe the answer is:
barred
'excluded' is the definition.
(I've seen this before)
'a bishop caught in the sack' is the wordplay.
'bishop' becomes 'rr' (abbreviation for Right Reverend).
'caught in' is an insertion indicator.
'the sack' becomes 'bed' ('in the sack' means 'in bed').
'a'+'rr'='arr'
'arr' placed inside 'bed' is 'BARRED'.
'is' is the link.
(Other definitions for barred that I've seen before include "Excluded, blocked" , "Refused entry to local pub" , "Refused access to, say pub" , "Wouldn't allow" , "Precluded, obstructed" .)