Run over a pack animal (4)
I believe the answer is:
wolf
'a 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' says the letters should be written in reverse.
'flow' back-to-front is 'WOLF'.
(Other definitions for wolf that I've seen before include "Pack-hunting carnivore" , "shovel down" , "philanderer" , "Dog-like animal - womaniser" , "Howling canine that hunts in packs" .)