Sorry fellow, below standard (6)
I believe the answer is:
pardon
'sorry' is the definition.
(I've seen this before)
'fellow below standard' is the wordplay.
'fellow' becomes 'don' (both can mean an academic).
'below' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'standard' becomes 'par' (standard of play in golf).
'don' put after 'par' is 'PARDON'.
(Other definitions for pardon that I've seen before include "Forgive the polite interruption" , "Excuse me, kindly overlook" , "Grant forgiveness" , "Forgive - eh?" , "Forgive; come again?" .)