The racket is in a different one (5)
I believe the answer is:
noise
'the racket' is the definition.
('noise' can be a synonym of 'racket')
'is in a different one' is the wordplay.
'in' means one lot of letters goes inside another.
'a different' is an anagram indicator.
'one' is an anagram of 'noe'.
'is' inserted inside 'noe' is 'NOISE'.
(Other definitions for noise that I've seen before include "Hubbub" , "Kind of pollution" , "Loud or disturbing sound" , "Confused sounds" , "Unwanted sound" .)