Morally, one's bound by beach volleyball's scoring? (4,2,3,4)

I believe the answer is:

line in the sand

I'm a little stuck... Click here to teach me more about this clue!

'volleyball's scoring?' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'morally one's bound by beach' is the wordplay.
'morally one' becomes 'inthe' (I can't justify this - if you can you should believe this answer much more).
'bound' becomes 'line' (both can mean a boundary).
'by' is a charade indicator (letters next to each other).
'beach' becomes 'sand'.
'inthe' after 'line' is 'lineinthe'.
'lineinthe'+'sand'='LINE IN THE SAND'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.