Predator needs run up (4)
I believe the answer is:
wolf
'predator' is the definition.
'run up' is the wordplay.
'run' becomes 'flow' (synonyms).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'flow' back-to-front is 'WOLF'.
'needs' acts as a link.
(Other definitions for wolf that I've seen before include "Pack animal; composer" , "Devour ravenously" , "Predatory canine animal" , "SECOND PART OF 14" , "See 2" .)