Whereupon the players have no seats? (9)
I believe the answer is:
bandstand
'whereupon the' is the definition.
I can't judge whether this definition defines the answer.
'players have no seats?' is the wordplay.
'players' becomes 'band' (group playing music).
'have' means one lot of letters go next to another.
'no seats?' becomes 'stand' (stand is a kind of seats. I am not sure about the 'no' bit.).
'band'+'stand'='BANDSTAND'
Can you help me to learn more?
(Other definitions for bandstand that I've seen before include "Outdoor music platform" , "place to play?" , "Outdoor platform for musical performances etc" , "Outdoor concert stage" , "park feature?" .)