Bird that’s foolishly trapped, once having flown in (9)
I believe the answer is:
stonechat
'bird' is the definition.
(stonechat is a kind of bird)
'foolishly trapped once having flown in' is the wordplay.
I cannot really see how this works, but
an anagram of 'once' is 'onec' which is within the answer.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for stonechat that I've seen before include "Heathland songbird" , "Small heathland bird" , "singer" , "Bird of thrush family" .)