One stuck in rising mire at Sweden's sports venue (7)
I believe the answer is:
stadium
'sports venue' is the definition.
(I've seen this before)
'one stuck in rising mire at sweden's' is the wordplay.
'one' becomes 'i' (Roman numeral).
'stuck in' means one lot of letters goes inside another.
'rising' says the letters should be written backwards (in a down clue, letters go up).
'mire' becomes 'mud' (synonyms).
'sweden' becomes 's'.
'mud'+'at'+'s'='mudats'
'mudats' back-to-front is 'stadum'.
'i' inserted into 'stadum' is 'STADIUM'.
(Other definitions for stadium that I've seen before include "Open-air sports venue" , "Large structure for open-air sports" , "eg Yankee, Wembley" , "A major sports ground" , "Venue for sporting events, concerts etc" .)