Rook stops fighting cock near grassland bird (9)
I believe the answer is:
corncrake
'grassland bird' is the definition.
(bird that lives in grassland)
'rook stops fighting cock near' is the wordplay.
'rook' becomes 'R' (chess abbreviation).
'stops' means one lot of letters goes inside another (stopping can mean blocking a gap).
'fighting' is an anagram indicator.
'cock'+'near'='cocknear'
'cocknear' is an anagram of 'corncake'.
'r' inserted into 'corncake' is 'CORNCRAKE'.
(Other definitions for corncrake that I've seen before include "Bird" , "kind of rail" .)