Game girl, good at heart (5)
I believe the answer is:
rugby
'game' is the definition.
(rugby is a sport or game)
'girl good at heart' is the wordplay.
I cannot quite see how this works, but
'girl' could be 'g' and 'g' is present in the answer.
The remaining letters 'ruby' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rugby that I've seen before include "Game named after school" , "Team sport" , "Team game" , "Ball-game" , "Tom Brown's school" .)