Fabled loser (4)
I believe the answer is:
hare
'fabled loser' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hare that I've seen before include "Run with great speed" , "As mad as this March animal" , "Swift mammal" , "Sect: -- Krishna" , "Game, -- and hounds" .)