Emerging from vaults where entry is forbidden (3,2,6)
I believe the answer is:
out of bounds
'is forbidden' is the definition.
(thesaurus)
'emerging from vaults where entry' is the wordplay.
I cannot quite understand how this works, but
'from' could be 'un' (I've seen this in other clues) and 'un' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for out of bounds that I've seen before include "Off limits" , "like an exhausted kangaroo?" , "lying beyond field of play?" , "taboo" , "Skipper so exhausted" .)