Taken to court about smear that’s continuing (9)
I believe the answer is:
sustained
'continuing' is the definition.
('sustained' can be similar in meaning to 'continuing')
'taken to court about smear' is the wordplay.
'taken to court' becomes 'sued' ('sue' can be a synonym of 'take to court').
'about' is an insertion indicator.
'smear' becomes 'stain' ('stain' can be a synonym of 'smear').
'sued' going around 'stain' is 'SUSTAINED'.
'that's' acts as a link.
(Other definitions for sustained that I've seen before include "Kept going, supported" , "Steady" , "Kept (something) going" , "suffered" , "prolonged" .)