Huge size of football club, reportedly having above one million followers (9)
I believe the answer is:
immensity
'huge size' is the definition.
'immensity' can be an answer for 'size' (immensity is a kind of size). I am not certain of the 'huge' bit.
'football club reportedly having above one million followers' is the wordplay.
I cannot really see how this works, but
'club' could be 'y' (YMCA or YWCA commonly shortened) and 'y' is located in the answer.
'reportedly' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'million' could be 'm' (abbreviation) and 'm' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for immensity that I've seen before include "Hugeness" , "bulk!" .)