Riotous cheering around Western part of London (9)
I believe the answer is:
greenwich
'part of london' is the definition.
(London borough)
'riotous cheering around western' is the wordplay.
'riotous' indicates anagramming the letters.
'around' indicates putting letters inside.
'western' becomes 'w'.
'cheering' anagrammed gives 'greenich'.
'greenich' going around 'w' is 'GREENWICH'.
(Other definitions for greenwich that I've seen before include "somewhere in London" , "part of London" , "Prime meridian site" , "origin of time" , "London suburb associated with Mean Time" .)