Crowd eruption (4)
I believe the answer is:
roar
'crowd eruption' 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 "24 [BOOM]" , "Loud noise of angry bull" , "Make a loud noise" , "Zoom - prolonged cry" , "Jaguar, for example, emits this" .)