Scare involving ferry - it rocked (7)
I believe the answer is:
terrify
'scare' is the definition.
(I know that terrify is a more specific form of the action scare)
'ferry it rocked' is the wordplay.
'rocked' indicates anagramming the letters.
'ferry'+'it'='ferryit'
'ferryit' with letters rearranged gives 'TERRIFY'.
'involving' acts as a link.
(Other definitions for terrify that I've seen before include "Greatly frighten" , "Make very frightened" , "Scare badly" , "Get scared" , "Frighten badly" .)