Commenter on web rebuked about large representative figure (6,5)

I believe the answer is:

poster child

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'representative figure' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'commenter on web rebuked about large' is the wordplay.
'commenter on web' becomes 'poster' (I am not sure about this - if you are sure you should believe this answer much more).
'rebuked' becomes 'chid' ('chide' can be a synonym of 'rebuke').
'about' is an insertion indicator.
'large' becomes 'L' (eg in clothes sizes).
'chid' enclosing 'l' is 'child'.
'poster'+'child'='POSTER CHILD'

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