Stadium sound (4)
'stadium sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for roar that I've seen before include "The __ of the Greasepaint -- The Smell of the Crowd (1964 musical)" , "cheer" , "Noise of lion" , "Deep-throated cry" , "Jaguar, for example, emits this" .)
(Other definitions for hooray that I've seen before include "Yippee!" , "Shout of approval" , "Shout of joy (for Henry?)" , "Exclamation of joy or victory" , "Cheer" .)