The racket in a boarding school (3)
I believe the answer is:
'the racket' is the definition.
(both can mean a loud noise or disturbance)
'in a boarding school' is the wordplay.
'in' indicates the answer is hidden within the clue.
'DIN' is hidden in the letters of 'boarding school'.
(Other definitions for din that I've seen before include "Unwanted noise" , "Loud and long noise" , "commotion" , "Loud noise, racket" , "Too much noise" .)