Hey @harveythenerd, welcome to the site! Hope you enjoy your stay here!

A quick Google search shows that Sports Island was actually called Deca Sports in the original Japanese release, and there are already leaderboards for Deca Sports/Sports Island here. For future reference, in case you ever actually need to add a new game to the site, you can do so by going to this link, reading the giant block of text, and then filling out the form at the bottom of the page.

As for your second question, recording rules vary from leaderboard to leaderboard, so you should check with the rules of your particular game for any such requirement. In general, I think both using a capture card and recording your screen with a camera are fine, so long as the gameplay is clear and fully visible.

Hope this clears things up! If you have any other questions, please feel free to ask.