Surrounded by leaders of angry mob in demonstration (4)
I believe the answer is:
amid
'surrounded by' is the definition.
(amid means among or surrounded by)
'leaders of angry mob in demonstration' is the wordplay.
'leaders of' indicates taking the first letters.
The first letters of 'angry mob in demonstration' is 'AMID'.
(Other definitions for amid that I've seen before include "In the centre of" , "Within" , "Surrounded by" , "In the course of" , "A dim sort of preposition" .)