It’s completely legal for you to bet on sports with a land-based bookmaker, and it’s completely legal for you to bet with an online betting site. The only stipulation is that you must be at least 18 years of age.
While it is not necessarily legal to bet sports online in the United States, you, as the user, are in no danger of prosecution for placing sports wagers. It's a paradox, for sure, but one that has a decent set of legal precedents to back it up.
Online sports’ betting was made legal in the United States following the lifting of the Professional and Amateur Sports Protection Act from 1992. Ever since 1992 this law stood in place and prevented states from offering betting services. This was the case on all but four states that were granted full immunity.
Even when laws do apply strictly to online sports betting, these are used to go after the operators of the sites themselves and not the individual members of said sites. Online sports betting is legal in the United States, and it is fully regulated in a few states so far (i.e. Nevada, New Jersey, West Virginia).
Betting with friends on sports online is legal as long as you use offshore betting sites. There are certain federal laws that prevent sports betting sites from operating within the United States. The Wire Act of 1961 makes it illegal for those in the business of gambling to accept bets or provide assistance with the placement of sports wagers via wire communication facilities.
In addition, US players are permitted to access offshore sports betting sites in most states except in Washington where lawmakers have established state laws outlawing access to all forms of online gambling. Residents in every other state can legally access offshore sportsbooks without violating any type of state or federal laws.
All 50 states are accepted and legally allowed to play at this legal sports gamblingwebsite per the rules on the site. BetOnline caters to other international players as well, as evidence by deposit methods that apply only to international players not available to U.S. players.
Federally regulated sports betting would be so much easier. Unfortunately, this type of market doesn’t exist in America. You’re forced to deal with one and a half dozen states that each have their own laws on the matter. The one universal rule, though, is that you must be within a state to place online or live bets.