Mock small company very loudly (5)
I believe the answer is:
scoff
'mock' is the definition.
(scoff can mean to mock or tease)
'small company very loudly' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'company' becomes 'co' (abbreviation).
'very loudly' becomes 'ff' (short for fortissimo, 'very loud' in music).
's'+'co'+'ff'='SCOFF'
(Other definitions for scoff that I've seen before include "Jeer; eat greedily" , "Quickly swallow" , "Ridicule - guzzle" , "Speak derisively" , "Devour (informal)" .)