The NFL is throwing a flag on sports betting. 

It warned teams on Thursday that certain types of player-specific prop bets are now off-limits following recent federal criminal charges tied to illegal wagering activity in the NBA and MLB. 

In a memo sent to club executives, the league said that protecting “the integrity of the game” remains the NFL’s top priority amid the explosion of legalized online sports betting. 

There are four categories of props that the NFL now deems prohibited: inherently objectionable, officiating-related, determinable by one person in one play, and pre-determined.

These restrictions look to cease wagers that are “inherently risky” and “corrosive” to fan trust and club personnel safety — including bets tied to sensitive situations, officiating decisions, or outcomes known before a play even begins.

“From the earliest days of legal sports betting, we have recognized the particular risks associated with prop bets and the corrosive effect they have on fan perceptions,” the memo reads.

Sports betting partners do not offer markets for whether a kicker misses a field goal or a quarterback completes his first pass attempt, which fall under the “one person in one play” prohibition. “Pre-determined” prop bets are exemplified by whether a quarterback will start on a given week or if a team’s first play from scrimmage will be a run or pass.

Markets based upon cumulative stats or individual scoring events — such as receiving yards totals or an anytime touchdown scorer — will remain allowed.

The league has worked with both state regulators and betting partners to limit or prohibit these prop bets that are connected to the behavior in recent investigations, and it is updating its commercial agreements to reflect that stance.

Players received a league-wide briefing on the subject prop bets this week, reminding them that “prediction markets” remain a form of prohibited gambling activity.

The league is expanding education for players and staff, reinforcing existing restrictions in partnership with the NFLPA.

Earlier this week, Cleveland Guardians pitchers Luis Ortiz and Emmanuel Clase were hit with conspiracy charges for allegedly tipping off bettors about what pitches they’d throw.

This followed last month’s massive NBA gambling bust where Hall of Famer and Blazers coach Chauncey Billups, Heat guard Terry Rozier and former NBA player and coach Damon Jones were indicted for funneling inside info to sports bettors.