Its affiliate marketing ...
Fantasy sports, online bingo, casinos, sports books and whatever other product you can market. Clicking thru = 30-90 day or lifetime cookie. as NL mentioned ... as the person deposits into a casino or sports book, you as the affiliate are credited with that customer ... yielding you the affiliate either a profit share of all loss's or a one time commission.
So if you clicked through a sports book banner somewhere and your re-depositing money, the person hosting the banner is getting a 25-30% cut of your loss's ...
Oh yeah Fantasy sports has been determined by the courts to be a game of skill and is perfectly legal to wager real money on in the US ..... LOL