Writer considered unbalanced shut up (4-6,3)

I believe the answer is:

felt-tipped pen

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'writer' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'considered unbalanced shut up' is the wordplay.
'considered' becomes 'felt' (feel can mean to consider or think).
'unbalanced' becomes 'tipped' (I can't justify this - if you can you should give a lot more credence to this answer).
'shut up' becomes 'pen' (pen can mean to shut in or enclose).
'felt'+'tipped'+'pen'='FELT-TIPPED PEN'

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I've seen this clue in The Times.

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