First, your table structure needs some work. Using text fields, especially names, for primary keys is not recommended. You should use an autonumber field for your PKs. You also should have a table for player and another table for cards, linked on PlayerID. People names should be broken down into at least first and last. I generally use 5 fields for people names. Finally, you don't need BOTH sport and league as Foriegn keys in the Cards table. Since the league is specific to a sport, you can get the sport from the link between league and sport.
I don't see where you tried to implement the instructions in that article. There are no comboboxes on that form.
I suggest that you make the design changes I suggested and then try to implement the instructions. If you don't get it to work, then post a revised copy of your database with what you have done and we will try to help further.