Just before following a leader of men (4)
I believe the answer is:
mere
'just' is the definition.
('just' can mean 'mere' or 'only')
'before following a leader of men' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'following' is a charade indicator (letters next to each other).
'a leader of' suggests taking the first letters.
The initial letter of 'men' is 'm'.
'ere' put after 'm' is 'MERE'.
(Other definitions for mere that I've seen before include "President Hollande's mother?" , "Lake (poetic); Maori war club" , "DDwater" , "Lake (and nothing else?)" , "Lake; simple" .)