Crowd gathering together made a strong statement, initially (4)
I believe the answer is:
mass
'crowd' is the definition.
(I know that mass is a more specific form of the action crowd)
'gathering together made a strong statement initially' is the wordplay.
'gathering' is an insertion indicator (gather can mean to acquire or bring in).
'together' becomes 'a' (I am not sure about this - if you are sure you should believe this answer much more).
'initially' suggests taking the first letters.
The first letters of 'made strong statement' is 'mss'.
'a' put inside 'mss' is 'MASS'.
Can you help me to learn more?
(Other definitions for mass that I've seen before include "13 [BULK]" , "Widespread" , "Large number of people" , "Holy service" , "Heap; religious service" .)