Races round in shock (5)
I believe the answer is:
scare
'shock' is the definition.
(I know that alarm is a is a more specific form of the action of shock)
'races round' is the wordplay.
'round' indicates an anagram.
'races' is an anagram of '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" .)