Go into battle and win some ground (4,3,5)
I believe the answer is:
take the field
'go into' is the definition.
(I know that take the field is a type of go into)
'battle and win some ground' is the wordplay.
I cannot quite see how this works, but
'win' could be 'take' (taking is a kind of winning) and 'take' is present in the answer.
'ground' could be 'field' (field is a kind of ground) and 'field' is present in the answer.
The remaining letters 'the' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for take the field that I've seen is " go on a campaign".)