Neck injury (8)
I believe the answer is:
'neck injury' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for whiplash that I've seen before include "Sort of injury" , "result of car crash?" , "Injury to neck from jerk of head, as in car accident" , "Common neck injury in a car accident" , "inflicted by cat" .)