Sporting venue taking an age to go round (5)
I believe the answer is:
arena
'sporting venue' is the definition.
(sports arena)
'an age to go round' is the wordplay.
'age' becomes 'era' (both can mean a long time).
'to go round' says the letters should be written in reverse (I've seen 'going round' mean this).
'an'+'era'='anera'
'anera' reversed gives 'ARENA'.
'taking' is the link.
(Other definitions for arena that I've seen before include "Area of endeavour" , "Sporting venue enclosed by seats" , "park" , "Space for public events" , "domain" .)