Pack animal run over (4)
I believe the answer is:
wolf
'pack animal' is the definition.
(I've seen this before)
'run over' is the wordplay.
'run' becomes 'flow' ('flow' can be a synonym of 'run').
'over' is a reversal indicator.
'flow' written backwards gives 'WOLF'.
(Other definitions for wolf that I've seen before include "Seducer - gobble down" , "Howling canine that hunts in packs" , "22A [WILD DOG]" , "Austrian composer" , "Carnivore -- breed of 13 down" .)