Inexperienced fellow mentioned stock market activity (9)

I believe the answer is:

greenmail

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'stock market activity' is the definition.
(type of stock market strategy)

'inexperienced fellow' is the wordplay.
'inexperienced' becomes 'green' (similar in meaning).
'fellow' becomes 'mail' (I am not sure about this - if you are sure you should believe this answer much more).
'green'+'mail'='GREENMAIL'

'mentioned' acts as a link.
This may not be right. It may belong to another bit of the clue.

Can you help me to learn more?

(Another definition for greenmail that I've seen is " dubious business practice".)

I've seen this clue in The Independent.

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