Who’s suggested an outdoor arena? (10)
I believe the answer is:
showground
'who's suggested' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'outdoor arena?' is the wordplay.
'outdoor' becomes 'show' (I am not sure about this - if you are sure you should believe this answer much more).
'arena?' becomes 'ground' (I've seen this before).
'show'+'ground'='SHOWGROUND'
'an' acts as a link.
Can you help me to learn more?
(Other definitions for showground that I've seen before include "Land for displays" , "Venue for exhibition" .)