Key leader removed fencing — bitter shock? (7)
I believe the answer is:
startle
'shock?' is the definition.
(I know that startle is a type of ball over)
I don't understand the remainder of the clue.
(Other definitions for startle that I've seen before include "Surprise with fright" , "Take unawares with rattles" , "Alarm (someone)" , "Scare" , "Surprise with starlet" .)