BetMGM, Caesars and DraftKings were first-movers on national spots promoting their sportsbook apps during the NFL’s season opener on NBC, spending to reach the masses even though only 30% of U.S. adults over 21 can bet legally from home. Here are the number of TV households in the top 10 U.S. TV markets. Only three, which are in bold, are in states that have legalized betting.