Fed up over preliminary race — not the first bad result in sport (6)
I believe the answer is:
defeat
'fed up over preliminary race not the first bad result in sport' is the definition.
I can't tell whether this defines the answer.
'over preliminary race not the first bad result in sport' is the wordplay.
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'preliminary race' becomes 'heat' (I've seen this before).
'not the first' means to remove the first letter.
'bad result' becomes 'D' (an exam result).
'in sport' becomes 'ef' (I can't explain this - if you can you should give a lot more credence to this answer).
'heat' with its first letter taken off is 'eat'.
'd'+'ef'='def'
'eat' after 'def' is 'DEFEAT'.
Can you help me to learn more?
(Other definitions for defeat that I've seen before include "Conquest" , "Get the better of" , "Unsuccessful ending" , "Beat (an opponent)" , "annulment" .)