Level, but the race hasn't finished (4)
I believe the answer is:
even
'level' is the definition.
(I know that level can be written as even)
'the race hasn't finished' is the wordplay.
'the race' becomes 'event' (I've seen this before).
'hasn't finished' means to remove the last letter.
'event' with its last letter removed is 'EVEN'.
'but' is the link.
(Other definitions for even that I've seen before include "Regular; calm" , "Quits - flat" , "Level, equal" , "Iron - uniform - flat" , "Equally balanced; level" .)