Supporter runs behind leader in battle (6)
I believe the answer is:
braces
'supporter' is the definition.
(thesaurus)
'runs behind leader in battle' is the wordplay.
'runs' becomes 'races' ('race' can be a synonym of 'run').
'behind' says to put letters next to each other.
'leader in battle' becomes 'b' (I can't explain this - if you can you should believe this answer much more).
'races' after 'b' is 'BRACES'.
Can you help me to learn more?
(Other definitions for braces that I've seen before include "Straps used to keep trousers up" , "Trouser support" , "bolsters" , "Props or trouser-supporters" , "Couples" .)