The rules on official betting in professional sports are strict. Athletes and their immediate family members cannot place wagers on events that they play in or officiate, and they are prohibited from seeking, offering, accepting, or agreeing to accept a bribe to fix a match or an event within a match. They are also banned from misusing inside information that could reasonably be used for betting purposes.

Joseph Sullivan, a bookmaker and gambler from Boston, Massachusetts, was the man behind one of the biggest betting scandals in sports history—the 1919 Black Sox Scandal, where he paid eight White Sox players (Oscar Felsch, Arnold Gandil, Shoeless Joe Jackson, Fred McMullin, Charles Risberg, George Weaver, Claude Williams, and Jimmy Cannon) to lose the World Series. The scandal led to the banning of these baseball players from the game forever.

In baseball, the sport’s governing body has a rule called “Rule 21” that prohibits players and their team staff from gambling on games that they play or officiate. People who violate this rule are permanently banned from the game, although many have been reinstated by a later commissioner.

The NHL hasn’t taken a public position on legal sports betting, but the Vegas Golden Knights have signed a sponsorship deal with William Hill that includes a sportsbook. Other professional clubs in states that have legalized sports betting are doing similar deals with bookmakers.