I have a league sports fixtures & results page, which has a number of matches listed, and I need to allow my users to comment on each match in a separate Remarkbox instance (on the same page).
Yes, Remarkbox can support this!
You will need to modify the "client" code with an additional identifier. By default the identifier is the parent window's URL. To support multiple Remarkbox instances per page, you would need something like URL + Match-id. I would be glad to support you in this integration.