Deadlock involving old friend (9)
I believe the answer is:
stalemate
'deadlock' is the definition.
(I know that deadlock can be written as stalemate)
'old friend' is the wordplay.
'old' becomes 'stale' (similar in meaning).
'friend' becomes 'mate' (mate is a kind of friend).
'stale'+'mate'='STALEMATE'
'involving' acts as a link.
(Other definitions for stalemate that I've seen before include "Chess game deadlock" , "Possible chess game ending" , "situation without a winner" , "A no-win situation in chess" , "a position on board" .)