Shade aggressive, knight knocked out (6)
I believe the answer is:
violet
'shade' is the definition.
(I know that violet is a shade)
'aggressive knight knocked out' is the wordplay.
'aggressive' becomes 'violent' (I've seen this before).
'knight' becomes 'N' (chess abbreviation).
'knocked out' is a deletion indicator.
'violent' with 'n' taken out is 'VIOLET'.
(Other definitions for violet that I've seen before include "See 9" , "William's girl" , "A flower for a girl" , "Mauve" , "Colour; flower, source of fragrance" .)