Defence is behind in bona fide case (8)
I believe the answer is:
rebuttal
'defence' is the definition.
(I know that rebuttal is a type of defence)
'behind in bona fide case' is the wordplay.
I cannot quite see how this works, but
'behind' could be 'butt' (both can mean the buttocks) and 'butt' is found in the answer.
'bona fide' could be 'real' (I've seen this in another clue) and 'real' is located in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for rebuttal that I've seen before include "reply to accusation" , "statement delivered to counter" , "resistance to attack" , "Confutation" , "Answer" .)