Impasse as bay abandons horse from the same yard (9)
I believe the answer is:
stalemate
'impasse' is the definition.
(I know that impasse can be written as stalemate)
'bay abandons horse from the same yard' is the wordplay.
'bay' becomes 'b' (horseracing abbreviation).
'abandons' is a deletion indicator.
'horse from the same yard' becomes 'stablemate' (another horse from the same stable).
'stablemate' with 'b' removed is 'STALEMATE'.
'as' is the link.
(Other definitions for stalemate that I've seen before include "Possible outcome of chess game" , "a position on board" , "Deadlock, impasse" , "where moving is impossible" , "Blocked position" .)