Open line ends shock (7)
I believe the answer is:
startle
'shock' is the definition.
(I know that startle is a more specific form of the action shock)
'open line ends' is the wordplay.
'open' becomes 'start' (I've seen this before).
'ends' says to hollow out the word (remove centre letters).
'line' with its middle removed is 'le'.
'start'+'le'='STARTLE'
(Other definitions for startle that I've seen before include "Rattles (anag.)" , "Surprise with starlet" , "Surprise with fright" , "Alarm (someone)" , "Rock" .)