Volume of unruly mobs in uniform (7)
I believe the answer is:
omnibus
'volume' is the definition.
(I have seen 'Compendium volume ' mean 'omnibus' so perhaps 'volume' could also mean 'omnibus')
'unruly mobs in uniform' is the wordplay.
'unruly' indicates anagramming the letters.
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'mobs'+'in'+'u'='mobsinu'
'mobsinu' with letters rearranged gives 'OMNIBUS'.
'of' is the link.
(Other definitions for omnibus that I've seen before include "Old vehicle - volume of works" , "collection of novels?" , "PSV" , "Book of collected works - vehicle" , "Comprehensive collection of books" .)