Raging Bull's origin hidden in attack (5)
I believe the answer is:
rabid
'raging' is the definition.
(I've seen this in another clue)
'bull's origin hidden in attack' is the wordplay.
'origin' suggests taking the first letters.
'hidden in' is an insertion indicator.
'attack' becomes 'raid' (raid is a kind of attack).
The first letter of 'bulls' is 'b'.
'b' placed within 'raid' is 'RABID'.
(Other definitions for rabid that I've seen before include "Mad like deranged dog" , "Fanatical like mad dog" , "Zealous" , "Ferocious" , "Fanatical, infected" .)