Excuse in court excellent defending one bishop on line (5)
I believe the answer is:
alibi
'excuse in court' is the definition.
(I've seen this before)
'excellent defending one bishop on line' is the wordplay.
I cannot really understand how this works, but
'one' could be 'li' (I've seen this in other clues) and 'li' is found within the answer.
'bishop' could be 'b' (chess abbreviation) and 'b' is located in the answer.
'excellent' could be 'ai' (resembles 'A1', old-fashioned term for excellent) and 'ai' is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for alibi that I've seen before include "Pretext; court excuse" , "Defence against charge - was seen elsewhere" , "Defence against accusation - was seen elsewhere at the time" , "Legal defence proving innocence" , "Legal defence, plea" .)