Bishop left unconscious in error (7)
I believe the answer is:
blunder
'error' is the definition.
(I know that error can be written as blunder)
'bishop left unconscious' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'left' becomes 'l' (common abbreviation).
'unconscious' becomes 'under' (as in under anaesthetic).
'b'+'l'+'under'='BLUNDER'
'in' is the link.
(Other definitions for blunder that I've seen before include "Stupid mistake" , "A stupid 1 down" , "Embarrassing mistake" , "A clumsy mistake or movement" , "Clumsy mistake, gaffe" .)