The NFL sent a memo to team officials Thursday to reemphasize the league’s stance on what types of wagers are permitted with its sportsbook partners, specifically calling out certain prop bets, which have come under increased scrutiny in recent weeks following the federal indictments of MLB and NBA players.

In the memo, the league says it has “actively engaged with both state lawmakers and regulators, as well as with our sports betting partners, to limit — and where possible prohibited altogether — prop bets in the NFL.”

The memo breaks down these prohibited wager categories as those that are inherently objectionable (i.e. player injuries, fan misconduct), officiating-related (officiating assignments, penalties, etc.), determinable by one person in one play (i.e. a quarterback’s first pass attempt to be incomplete) and predetermined (events that could be determined before a game is played).

Legal sportsbooks in the United States generally have not offered these types of bets in the past anyway and it is not anticipated that Thursday’s memo will force any changes to their offerings.

The memo specifically states that the league considers the use of prediction markets — such as Kalshi and Polymarket — to be “prohibited gambling activity.” It also includes a reminder of rules for NFL personnel under the league’s gambling policy, as well as the measures the league has taken to maintain the integrity of the game as it relates to sports betting.

The NFL has largely managed to avoid integrity concerns. While a member of the Atlanta Falcons, Tennessee Titans wide receiver Calvin Ridley was suspended for the entire 2022 season after he bet on games during the 2021 season, including on his own team. Ahead of the 2023 campaign, several players, including Detroit Lions receiver Jameson Williams, were suspended for varying lengths of time for their own violations of the league’s gambling policy.

Recent controversies in MLB and the NBA could have prompted the league to reaffirm its position on certain types of prop bets.