Competitive horse level with leaders in the Epsom race (7)
I believe the answer is:
eventer
'competitive horse' is the definition.
(I've seen this before)
'level with leaders in the epsom race' is the wordplay.
'level' becomes 'even' (synonyms).
'with' is a charade indicator (letters next to each other).
'leaders in' says to take the initial letters.
The first letters of 'the epsom race' is 'ter'.
'even'+'ter'='EVENTER'
(Other definitions for eventer that I've seen before include "Equestrian competitor" , "Jumper" , "Competitive horse/rider" , "Competitive rider" , "Sportsman" .)