Best unable to play the game? (9)
I believe the answer is:
matchless
'best' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for matchless that I've seen before include "team without a fixture" , "Second to none" , "Without a rival" , "reason for rubbing sticks together?" , "beyond compare" .)