Greatest striker, marker after shirt, say? (3,6)

I believe the answer is:

top scorer

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

'greatest striker marker' is the definition.
I know nothing about this answer so I can't tell whether this works.

'after shirt say?' is the wordplay.
'after' says to put letters next to each other.
'shirt' becomes 'top' (I've seen this in another clue).
'say?' becomes 'scorer' (I can't explain this - if you can you should give a lot more credence to this answer).
'top' next to 'scorer' is 'TOP SCORER'.

Can you help me to learn more?

I've seen this clue in The Guardian.

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.