Belittle - it angered assembly (9)
I believe the answer is:
denigrate
'belittle' is the definition.
(I know that belittle can be written as denigrate)
'it angered assembly' is the wordplay.
'assembly' indicates an anagram.
'it'+'angered'='itangered'
'itangered' anagrammed gives 'DENIGRATE'.
(Other definitions for denigrate that I've seen before include "Bad-mouth" , "Defame" , "put down" , "Slight" , "Run down" .)