Line gained ground at the front (7)
I believe the answer is:
leading
'the front' is the definition.
(I've seen this before)
'line gained ground' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'ground' indicates an anagram ('grind' the letters into a new form).
'gained' with letters rearranged gives 'eading'.
'l'+'eading'='LEADING'
'at' acts as a link.
(Other definitions for leading that I've seen before include "Guiding by going in front" , "In the chair" , "Most important; ahead" , "Principal" , "Prominent" .)