Predator going backwards in stream (4)
I believe the answer is:
flow
'stream' is the definition.
(I know that stream can be written as flow)
'predator going backwards' is the wordplay.
'predator' becomes 'wolf'.
'going backwards' says the letters should be written backwards.
'wolf' back-to-front is 'FLOW'.
'in' acts as a link.
(Other definitions for flow that I've seen before include "Fluid motion" , "Scapa - , Orkney anchorage" , "Current" , "Move steadily" , "Run smoothly" .)