Silly trick in PE leaves one in critical condition (3-6)

I believe the answer is:

nit-picker

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'one in critical condition' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'silly trick in pe' is the wordplay.
'silly' is an anagram indicator.
'trick'+'in'+'pe'='trickinpe'
'trickinpe' with letters rearranged gives 'NIT-PICKER'.

'leaves' acts as a link.

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