Heads round front of battle lines (7)
I believe the answer is:
obverse
'heads' is the definition.
(thesaurus)
'round front of battle lines' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'front of' indicates taking the first letters.
'lines' becomes 'verse' (I've seen this before).
The first letter of 'battle' is 'b'.
'o'+'b'+'verse'='OBVERSE'
(Other definitions for obverse that I've seen before include "Side normally seen" , "One side of a coin" , "Heads as opposed to tails" , "Penny may present such a face" , "Coin's head side" .)