Is included among those against rackets (6)
I believe the answer is:
noises
'rackets' is the definition.
('noise' can be a synonym of 'racket')
'is included among those against' is the wordplay.
'included' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'among' is an insertion indicator.
'those against' becomes 'nos' (I've seen this in another clue).
'is'+'e'='ise'
'ise' inserted into 'nos' is 'NOISES'.
Can you help me to learn more?
(Other definitions for noises that I've seen before include "sounds unpleasant" , "Unmusical sounds?" , "Spreads abroad with sounds" , "Sounds, rackets" , "- - Off (stage farce)" .)