Hawk grabbing river fish (5)
I believe the answer is:
trout
'fish' is the definition.
(I know that trout is a type of fish)
'hawk grabbing river' is the wordplay.
'hawk' becomes 'tout' (I've seen this in another clue).
'grabbing' is an insertion indicator.
'river' becomes 'r' (abbreviation for river).
'tout' enclosing 'r' is 'TROUT'.
(Other definitions for trout that I've seen before include "Tutor (anag.)" , "Mistiness" , "Fish - old harridan" , "Tickled fish?" , "Schubert work; fish" .)