As a game that is set-up like an actual sports type event, I think you should have the ability to have a spectator mode. The spectator people could have their own roster, so even if the game is full, unless it's full of spectators they could still join. Make the limit like maybe 3 or 4, so it's not too much more. Then if someone leaves the game, you could just hop right in. This is just a creative idea I thought could be a future game-add on. I doubt there could really be any achievements involved though lol.