Equestrian competition unfinished still (4)
I believe the answer is:
even
'still' is the definition.
('even' can be a synonym of 'still')
'equestrian competition unfinished' is the wordplay.
'equestrian competition' becomes 'event'.
'unfinished' means to remove the last letter.
'event' with its last letter removed is 'EVEN'.
(Other definitions for even that I've seen before include "Plumb" , "Flat, regular" , "of consistent quality" , "Yet; level" , "Level, straight or regular" .)