Girl has old score (4)
I believe the answer is:
goal
'score' is the definition.
(I've seen this in another clue)
'girl has old' is the wordplay.
'girl' becomes 'gal' (synonyms).
'has' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'gal' enclosing 'o' is 'GOAL'.
(Other definitions for goal that I've seen before include "Aim (at football)" , "Aim or purpose" , "posts and bar" , "could be worth 3 points" , "Objective, purpose" .)