Mischievous child endlessly making racket (4)
I believe the answer is:
scam
'racket' is the definition.
(racket is a type of scam or scheme)
'mischievous child endlessly' is the wordplay.
'mischievous child' becomes 'scamp' (I've seen this before).
'endlessly' means to remove the last letter.
'scamp' with its final letter removed is 'SCAM'.
'making' is the link.
(Other definitions for scam that I've seen before include "An informal swindle" , "Fraudulent business scheme" , "fiddle" , "'A con, deception (4)'" , "Swindle (sl.)" .)