When a wild bear has a dizzy head, keep out! (5)

I believe the answer is:

debar

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'keep out' is the definition.
(to debar someone is to keep them out of something)

'when a wild bear' is the wordplay.
'when' becomes 'd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a wild' indicates an anagram.
'bear' anagrammed gives 'ebar'.
'd'+'ebar'='DEBAR'

'has a dizzy head' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for debar that I've seen before include "Refuse to admit" , "Shut out, preclude" , "Exclude (from right)" , "Black" , "Stop" .)

I've seen this clue in the Evening Standard.

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