Have to stop game in river (5,4)
I believe the answer is:
great ouse
'river' is the definition.
(I've seen this before)
'have to stop game' is the wordplay.
'have' becomes 'eat' (have can mean to eat or consume).
'to stop' means one lot of letters goes inside another (stop can mean to plug a hole in something).
'game' becomes 'grouse' (I've seen this before).
'eat' put into 'grouse' is 'GREAT OUSE'.
'in' acts as a link.
(Other definitions for great ouse that I've seen before include "Flower" , "Fens river" .)