Do battle with, to get the first course (8)
I believe the answer is:
consomme
'course' is the definition.
(I've seen this before)
'do battle' is the wordplay.
'do' becomes 'con' (both can mean to defraud).
'battle' becomes 'somme' (Battle of the Somme in WW1).
'con'+'somme'='CONSOMME'
'with to get the first' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for consomme that I've seen before include "Clear French meat soup" , "Clear soup made with concentrated stock" , "Thin, clear soup" , "liquid course" , "Clear soup usually of beef, veal or chicken" .)