Leader is poorly understood (8)
I believe the answer is:
Here is my best explanation:
'understood' is the definition.
(I've seen this before)
'leader is poorly' is the subsidiary indication.
'poorly' indicates anagramming the letters.
'leaderis' with letters rearranged gives 'realised'.
(Other definitions for realised that I've seen before include "Came to know", "Came to be aware", "Became fully aware of or converted into money", "Understood - cashed in", "Came to understand", "Sidereal (anag)", "Became aware of in sidereal way", "Cashed in", "Came to awareness" and "Fully comprehended".)