Leader is poorly understood (8)
I believe the answer is:
realised
'understood' is the definition.
('understood'->'realized' is in my internal thesaurus and 'ize'->'ise')
'leader is poorly' is the wordplay.
'poorly' is an anagram indicator.
'leader'+'is'='leaderis'
'leaderis' with letters rearranged gives 'REALISED'.
(Other definitions for realised that I've seen before include "Came to understand" , "Sidereal (anag)" , "Became fully aware of or converted into money" , "Achieved; red aisle (anag.)" , "Came to be aware" .)