Competitor withdrawing from race course after midday loses nothing (3-7)
I believe the answer is:
non-starter
'competitor withdrawing from race' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'course after midday loses nothing' is the wordplay.
'course' becomes 'starter' (course of a meal).
'after' means one lot of letters go next to another.
'midday' becomes 'noon' (synonyms).
'loses' indicates named letters should be taken away.
'nothing' becomes 'O' (O resembles 0).
'noon' with 'o' removed is 'non'.
'starter' put after 'non' is 'NON-STARTER'.
Can you help me to learn more?
(Other definitions for non-starter that I've seen before include "Something with no chance of success" , "Someone who is never going to succeed" .)