Leaderless soldiers take heart over extra performance (6)
I believe the answer is:
encore
'extra performance' is the definition.
(I've seen this before)
'leaderless soldiers take heart' is the wordplay.
'leaderless' means to remove the first letter.
'soldiers' becomes 'men' (men can mean a group of soldiers).
'take' is a charade indicator (letters next to each other).
'heart' becomes 'core' (synonyms).
'men' with its initial letter removed is 'en'.
'en'+'core'='ENCORE'
'over' is the link.
(Other definitions for encore that I've seen before include "Request for repeat performance" , "Cry from the audience for more" , "We need more" , "(Call for) repeat performance" , "Bis!" .)