The mount of a top contestant out to finish fast? (5)
I believe the answer is:
steed
'the mount' is the definition.
(steed is a kind of mount)
'contestant out to finish fast?' is the wordplay.
'contestant' becomes 'seed' (seed is a kind of contestant).
'out' is an insertion indicator.
'to finish' suggests the final letters.
The last letter of 'fast' is 't'.
'seed' enclosing 't' is 'STEED'.
'of a top' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for steed that I've seen before include "Stallion" , "Literary term for horse" , "Spirited horse" , "Horse, mount" , "A mount (poet.)" .)