Last observation leaving host out (7,4)

I believe the answer is:

parting shot

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'last observation' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'leaving host out' is the wordplay.
'leaving' becomes 'parting' (parting is a kind of leaving).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'host' with letters rearranged gives 'shot'.
'parting'+'shot'='PARTING SHOT'

Can you help me to learn more?

(Another definition for parting shot that I've seen is " Cutting remark on leaving".)

I've seen this clue in The Daily Express.

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