Sound final whistle in play (7)
I believe the answer is:
endgame
'play' is the definition.
(I've seen this before)
'sound final whistle' is the wordplay.
I cannot really understand how this works, but
'final' could be 'end' (synonyms) and 'end' is found in the answer.
The remaining letters 'game' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for endgame that I've seen before include "contest's final stage" , "moves before mating" , "Final stage in a contest" , "drama" , "closing stage" .)