Doing everything possible to have no blacklegs (3,3)

I believe the answer is:

all out

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'doing everything possible to have no blacklegs' is the definition.
I can't judge whether this defines the answer.

'doing everything possible to have no' is the wordplay.
'doing everything' becomes 'allo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'possible' becomes 'on' ('not on' can mean unacceptable or not possible).
'to' becomes 'unto' (I've seen this before).
'have no' is a deletion indicator.
'unto' with 'on' taken away is 'ut'.
'allo'+'ut'='ALL-OUT'

Can you help me to learn more?

(Other definitions for all out that I've seen before include "top speed" , "call for 6 [STRIKING]?" , "Putting full effort into" , "Determined" , "Complete" .)

I've seen this clue in the Evening Standard.

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