Spooner's going crazy about I, Claudius , perhaps (8)
I believe the answer is:
poisoner
'claudius perhaps' is the definition.
(Claudius poisoned Hamlet's father in Shakespeare)
'spooner's going crazy about i' is the wordplay.
'going crazy' indicates an anagram.
'about' means one lot of letters goes inside another.
'spooner' anagrammed gives 'posoner'.
'posoner' going around 'i' is 'POISONER'.
(Other definitions for poisoner that I've seen before include "Person who uses chemicals to kill" , "Eg, Dr Crippen" , "Murderer like Crippen" , "Dr Crippen, perhaps" , "Killer using a toxic substance" .)