The NFL asked prediction market operators such as Kalshi and Polymarket to refrain from offering trades on events that can be easily manipulated or determined in advance, including what announcers say during broadcasts, which celebrities attend games and the upcoming draft.

The NFL said it wanted to protect game participants from “unfair and unwanted allegations” tied to gambling and prediction markets and objected to four types of offerings: those that can be easily manipulated by a single person such as missed field goals, those that are knowable in advance such as draft picks, player signings and coach firings, anything related to officiating and “inherently objectionable” topics such as player injuries and fan safety.

Most of the NFL’s objections in the letter are similar to what it asks traditional sportsbooks to prohibit, but the league also raised concerns about trading on broadcaster mention markets and celebrity attendance, two propositions not usually offered by sportsbooks. Millions of dollars were traded on Kalshi on what announcers said and which celebrities appeared at the Super Bowl.

“Some people are going to have that information … that they can then share,” NFL executive vice president Jeff Miller told ESPN. “We’re trying to stay as far as we can from some of those sorts of inside information wagers that could exist in this space.”