The legality of gambling has been questioned for years, with fantasy football being no stranger to controversy. At its inception, fantasy football players were betting on sports, a practice that was outlawed in 49 states (Nevada). What differentiates fantasy football is that people are good at it. Since fantasy sports require skill rather than banking on luck like many casino games and other betting mediums, it is not disallowed.
Moreover, weekly fantasy sites like FanDuel and Draftkings have to be careful about the content that they allow to be bet on. As long as no bets are placed regarding the performance of a singular player or the outcome of a certain game then the Unlawful Internet Gambling Enforcement Act is not broken. A setback for the two most popular daily fantasy sites occurred when employees were caught winning money using information they had illegally obtained.
Despite its nationwide acceptance, states have begun to ban daily fantasy sports at the individual level. Arizona, Washington, Idaho, Nevada, Montana, Hawaii, Texas, Iowa, Louisiana, Delaware, and Alabama have all prohibited some type of fantasy play as of 2017.
The good news for fantasy fans is that sports betting as a whole has been gaining support and the federal law prohibiting it was defeated in 2018. This still allows states to set their own legislation preventing it, but the country appears to be turning into a pro-sports gambling and thus pro-fantasy football site.