Ardent leader of men behind struggle (4)
I believe the answer is:
warm
'ardent' is the definition.
(I've seen this before)
'leader of men behind struggle' is the wordplay.
'leader of' says to take the initial letters.
'behind' is a charade indicator (letters next to each other).
'struggle' becomes 'war' (warring is a kind of struggling).
The first letter of 'men' is 'm'.
'm' after 'war' is 'WARM'.
(Other definitions for warm that I've seen before include "Affectionate - balmy" , "easily aroused" , "Heated; enthusiastic" , "Showing affection" , "showing enthusiasm" .)