A federal appeals court on Monday dealt another body blow to Delaware's plans for a new sports betting lottery, saying it must be limited to parlay bets on professional football games.

A three-judge panel of the 3rd U.S. Circuit Court of Appeals declared last week that Delaware's sports betting plan, which included single-game bets and wagering on a variety of professional and collegiate sports, violated federal law but it did not expressly say why.

On Monday, the panel outlined its reasoning in a 23-page opinion. The court said it interpreted language that exempted Delaware from a 1992 federal ban on sports gambling — known as the Professional and Amateur Sports Protection Act — as precluding any type of betting beyond what it had offered in a failed National Football League lottery in 1976.

That lottery allowed only parlay bets, which means bettors had to pick the winners of at least three separate NFL games in a single wager.

"Thus, any effort by Delaware to allow wagering on athletic contests involving sports beyond the NFL would violate PASPA," Judge Thomas Hardiman wrote for the court. "It is also undisputed that no single-game betting was 'conducted' by Delaware in 1976, or at any other time during the time period that triggers the PASPA exception."