Alarm when the cut finger sprained (8)
I believe the answer is:
frighten
'alarm' is the definition.
(I know this)
'the cut finger sprained' is the wordplay.
'cut' means to remove the last letter.
'sprained' indicates an anagram (letters sprained or damaged).
'the' with its last letter taken away is 'th'.
'th'+'finger'='thfinger'
'thfinger' with letters rearranged gives 'FRIGHTEN'.
'when' acts as a link.
(Other definitions for frighten that I've seen before include "Put the wind up" , "Cause fear" , "Scare, alarm" , "Terrify" , "Cow" .)