In the four years since it was legalized, sports betting in the U.S. has pulled in over $125 billion and a lot of that has come from only a few sportsbooks. DraftKings (DKNG) is up +10.20% for the month of June while its close competitor, Caesars Sportsbook (CZR) trailed +9.68%. BetMGM and FanDuel are not publicly traded but each have played a role in achieving that number.