Maturity worked when ejecting leader of anarchic element (7)
I believe the answer is:
yttrium
'element' is the definition.
(yttrium is a kind of element)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for yttrium that I've seen before include "Chemical element; um, try it (anag.)" , "Metallic element, symbol Y" , "12 [ELEMENT]" , "Silvery metallic element" , "Table item" .)