Jostle; sudden shock (4)
I believe the answer is:
jolt
I believe this clue is a double definition.
'jostle' is the first definition.
(thesaurus)
'sudden shock' is the second definition.
(I've seen this before)
(Other definitions for jolt that I've seen before include "A sudden jar" , "Sudden jerk" , "elbow" , "Sudden shock" , "Shock, jerk" .)