Knocked out by a false step, perhaps (4,6)

I believe the answer is:

fast asleep

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'knocked out' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'a false step perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'a'+'false'+'step'='afalsestep'
'afalsestep' anagrammed gives 'FAST ASLEEP'.

'by' is the link.

Can you help me to learn more?

(Another definition for fast asleep that I've seen is " Slumbering soundly".)

I've seen this clue in the Sydney Morning Herald.

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