Unreal shot of the nervous system (6)
I believe the answer is:
neural
'of the nervous system' is the definition.
(I've seen this before)
'unreal shot' is the wordplay.
'shot' indicates an anagram.
'unreal' with letters rearranged gives 'NEURAL'.
(Other definitions for neural that I've seen before include "Relating to the nervous system" , "Relating to a nerve" , "Nervy" , "Relating to nerves" , "To do with nerve of unreal kind" .)