Ascot's finale after flat race? (5)
I believe the answer is:
event
'race?' is the definition.
(race is a kind of event)
'ascot's finale after flat' is the wordplay.
'finale' says to take the final letters.
'after' means one lot of letters go next to another.
'flat' becomes 'even' (level).
The final letter of 'ascot' is 't'.
't' after 'even' is 'EVENT'.
(Other definitions for event that I've seen before include "celebration?" , "'Occurrence, happening (5)'" , "major incident" , "Something that happens - part of a programme?" , "Particular happening" .)