Attack in trouble after a case of shingles (6)
I believe the answer is:
assail
'attack' is the definition.
('assail' can be a synonym of 'attack')
'trouble after a case of shingles' is the wordplay.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble').
'after' is a charade indicator (letters next to each other).
'case of' says to hollow out the word (remove centre letters) (outsides of).
'shingles' with its middle removed is 'ss'.
'a'+'ss'='ass'
'ail' put after 'ass' is 'ASSAIL'.
'in' is the link.
(Other definitions for assail that I've seen before include "Trouble" , "Go for" , "Attack violently and persistently" , "Criticize" , "Slate" .)