It was advertised as a way to make custom online teams using your favorite players from across the sport (whichever sport you’re playing). What it actuallly does is turn sports games into gacha games by having the players you want for your custom team locked behind card packs. Some games go the extra step of having the good cards work for a limited number of games. Cards can be purchased either with in-game currency that you earn slowly or with real-world currency.