Shock following fit (6)
I believe the answer is:
fright
'shock' is the definition.
(I've seen this before)
'following fit' is the wordplay.
'following' becomes 'f.' (used when citing page numbers etc).
'fit' becomes 'right' (I've seen this before).
'f'+'right'='FRIGHT'
(Other definitions for fright that I've seen before include "Horror" , "A scare or shock" , "Sudden exposure to fear" , "Alarming event" , "Terror" .)