Once again understood leader must become adult (4)
I believe the answer is:
anew
'once again' is the definition.
(I've seen this in another clue)
'understood leader must become adult' is the wordplay.
I cannot really understand how this works, but
'adult' could be 'a' (abbreviation) and 'a' is found in the answer.
The remaining letters 'new' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for anew that I've seen before include "Afresh" , "Once more (poetic)" , "From the beginning again" , "Again but differently" , "Wane in a different way, again" .)