O'Riordan plays without a rook? What sort of game is this? (6)
I believe the answer is:
indoor
'o'riordan plays' is the definition.
I can't tell whether this definition defines the answer.
'without a rook? what sort of game is this?' is the wordplay.
I cannot quite see how this works, but
'rook?' could be 'do' and 'do' is located in the answer.
'without' could be 'no' and 'no' is found in the leftover letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for indoor that I've seen before include "Not in the open air, maybe sport" , "covered" , "Under a roof, like some sports" , "Sport like snooker, darts or badminton" , "For use in buildings" .)