Gathering clamour breaks record (5)
I believe the answer is:
crowd
'gathering' is the definition.
(crowd is a kind of gathering)
'clamour breaks record' is the wordplay.
'clamour' becomes 'row'.
'breaks' is an insertion indicator.
'record' becomes 'cd' (I've seen this in other clues).
'row' inserted inside 'cd' is 'CROWD'.
(Other definitions for crowd that I've seen before include "Spectators" , "Social set" , "Flock" , "Large number of people gathered together" , "Throng" .)