Spooner's top unruly youth once put on trial here? (4,3)
I believe the answer is:
test bed
'spooner's top unruly youth once put on trial here?' is the definition.
The definition suggests a singular noun which matches the answer.
'put on trial here?' is the wordplay.
I cannot really see how this works, but
'put' could be 'bed' (bedding is a kind of putting) and 'bed' is found within the answer.
'trial' could be 'test' (synonyms) and 'test' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for test bed that I've seen before include "place for experimental trials" , "engineers are working on it" , "Practise sleeping" , "trial equipment" .)