Put down for an indoor game (6)
I believe the answer is:
squash
'game' is the definition.
(squash is a kind of game)
'put down for an indoor' is the wordplay.
'put down' becomes 'quash' (both can mean to suppress or stop).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'an indoor' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
'quash' after 's' is 'SQUASH'.
Can you help me to learn more?
(Other definitions for squash that I've seen before include "Fruit - drink - crush" , "Crush, squelch" , "Compress" , "Fruit drink; a ball game" , "Vegetable on court?" .)