The Colosseum, for one (5)
I believe the answer is:
arena
'the colosseum for one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arena that I've seen before include "Where one may find sportsmen" , "battlefieId" , "bowl? Possibly" , "Wembley, for example" , "Sports or entertainment venue" .)