Races round in shock (5)
I believe the answer is:
scare
'shock' is the definition.
(I know that shock is a more specific form of alarm)
'races round' is the wordplay.
'round' indicates anagramming the letters.
'races' with letters rearranged gives 'SCARE'.
'in' is the link.
(Other definitions for scare that I've seen before include "Greatly frighten" , "Startle" , "Cause fright, alarm" , "Panic" , "Frighten or intimidate" .)