Youngster turned out for walk in park (6,4)
I believe the answer is:
childs play
'walk in park' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'youngster turned out' is the wordplay.
'youngster' becomes 'child' (synonyms).
'turned out' becomes 'splay' (I can't explain this - if you can you should believe this answer much more).
'child'+'splay'='CHILDS-PLAY'
'for' is the link.
Can you help me to learn more?
(Other definitions for childs play that I've seen before include "A piece of cake" , "A thing that's very easy to do" , "A doddle" , "A dramatisation of the nativity" , "Something very easy to do" .)