Screen 1: App Icon (1024x1024)
Needs to be bright and feature a prominent dollar sign and football. It should also feature a baseball, soccer ball, and basketball. Attention grabbing to stand out from other apps in the App Store.
Screen 2: Game Selection
Table of games, two columns, competing teams in each row. Include game time, some brief text about the game's odds, and team logos. Team logos could be integrated in the background.
Screen 3: Bet Selection
Six buttons total.
Team bets: Bet on either team to beat the spread or to beat the other team.
Non-team bets: Bet "Under" or "Over" a combined point total for both teams.
Screens 2 and 3 should have a header with banked money and in play money values. Tapping those sections will bring up an In-App Purchase modal box that is not part of this contest (but you might want to make those sections look "button-ey").
There also will be either a side menu or breadcrumbs to navigate. You don't have to design the side menu but if your design expects one there should be something in the header to expose it (used in addition to a swipe gesture). If you use breadcrumbs then the header would be a good place for it, but feel free to get creative. The breadcrumbs would be something like "Home > Basketball > NBA".