Mixture of large men rioting leaving Reading (7)
I believe the answer is:
melange
'mixture' is the definition.
(I know that melange is a type of mixture)
I can't explain the remainder of the clue.
(Other definitions for melange that I've seen before include "Gallimaufry" , "Medley" , "A French blend or mixture" , "A motley assortment of things" , "Confusion" .)