Big hit, singer's first record (4)
I believe the answer is:
slog
'big hit' is the definition.
(I've seen this before)
'singer's first record' is the wordplay.
'singer's first' becomes 's' (1st letter of 'singer').
'record' becomes 'log' (log is a kind of record).
's'+'log'='SLOG'
(Other definitions for slog that I've seen before include "Exhausting task" , "Long tedious task" , "almighty wallop" , "Very tiring work" , "Hit hard - hard trek" .)