Shaking in one's boots from a loud attack (6)
I believe the answer is:
afraid
'shaking in one's boots' is the definition.
(I've seen this in another clue)
'a loud attack' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'attack' becomes 'raid' (raid is a kind of attack).
'a'+'f'+'raid'='AFRAID'
'from' acts as a link.
(Other definitions for afraid that I've seen before include "Nervous" , "Frightened" , "Regretfully" , "cowardly" , "Feeling anxiety or fear" .)