When caught, all but the novice snarled! (6)

I believe the answer is:

snared

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'when caught' is the definition.
'snared' can be an answer for 'caught' (snaring is a kind of catching). I am unsure of the 'when' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for snared that I've seen before include "Caught in trap as by poacher" , "Caught in a trap like rabbit in noose" , "Enticed and trapped" , "Entrapped" , "Trapped by sander" .)

I've seen this clue in the Evening Standard.

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