What big, year-round op sorted out (1,3,4,6)
I believe the answer is:
i beg your pardon
'what' is the definition.
(I've seen this before)
'big year-round op sorted out' is the wordplay.
'sorted out' indicates an anagram.
'big'+'year'+'round'+'op'='bigyearroundop'
'bigyearroundop' with letters rearranged gives 'I BEG YOUR PARDON?'.
(Other definitions for i beg your pardon that I've seen before include "come again" , "Sorry" , "Please forgive me" , "let me off, please" .)