Fanatical attack involving bishop (5)
I believe the answer is:
rabid
'fanatical' is the definition.
(I know that fanatical can be written as rabid)
'attack involving bishop' is the wordplay.
'attack' becomes 'raid' (raid is a kind of attack).
'involving' is an insertion indicator.
'bishop' becomes 'B' (chess abbreviation).
'raid' enclosing 'b' is 'RABID'.
(Other definitions for rabid that I've seen before include "Fanatical, infected" , "Extremely fanatical" , "Extreme, fanatical" , "Affected by hydrophobia" , "Ferocious" .)