He was also a pretty fair boxer back in the day, and settled more law enforcement problems with his fists than he ever did with a gun. He had, in fact, refereed 30-some fights when he was younger, though under London Prize Ring Rules, and not the Marquess of Queensberry Rules. (The difference being that the London rules were written for bare-knuckle fighting, and allowed for holds and throws.)
So when Bob Fitzsimmons and Tom Sharkey met for the heavyweight title in San Francisco in 1896 and neither side could agree on a referee, one of the promoters suggested Wyatt Earp, who just happened to be in town. "I knew that Wyatt Earp was a cool, clear-headed person of unimpeachable reputation, and one who would be perfectly fair to both fighters," he said. "Wyatt Earp was the bravest fighter, the squarest gambler, the best friend, and the worst enemy ever known on the frontier."
A little florid, maybe, but Wyatt shrugged and said, Sure, okay... A decision he regretted for the rest of his life.
Fitzsimmons (at right) was the champ and was heavily favored to win. He was a Brit from Cornwall, and one of the hardest punchers in boxing history.
So to cut to the chase... Fitzsimmons was bigger and faster than Sharkey, and took charge of the fight from the opening bell. In the 8th, with the two fighters punching and counter punching so close in that nobody had a good view of it, Fitzsimmons threw a low, right-hand uppercut that sent Sharkey to the canvas clutching himself and screaming foul. Fitzsimmons, he claimed, had hit him in the groin.
Wyatt stopped the fight and sent both men to their corners. After a brief conference with each, he disqualified Fitzsimmons on a foul, and ruled that Sharkey was the new heavyweight champion of the world. Instant chaos. Boos and catcalls from a crowd of 15,000 that had largely bet on Fitzsimmons. Wyatt slipped like Elvis quickly out of the building.
The two major San Francisco newspapers took opposing views of Wyatt Earp as a referee. (Kind of like the way two newspapers took different sides in Tombstone.) The Examiner loudly supported Wyatt, but The San Francisco Call attacked him bitterly, saying that he was either blind or a fool, and even claiming that he had bet on Sharkey and was in on a fix. It was a hell of a mess. Fitzsimmons filed an injunction to stop the payout of the purse, Sharkey's side countersued, and the District Attorney threatened to convene a grand jury. Nobody happy except the Sharkey bettors because the books went ahead and paid off.
Sharkey retained the title until James J. Corbett came out of retirement. Fitzsimmons subsequently knocked out Corbett and himself regained the heavyweight title in 1897. Wyatt Earp left San Francisco and didn't return until he booked passage on a boat to Alaska a year or so later.
Postscript: Eight years after the fight, one of Sharkey's corner men, a Dr. B. Brookes Lee, admitted that he had treated Sharkey to make it appear that he had been fouled. He said, "I fixed Sharkey up to look as if he had been fouled. How? Well, that is something I do not care to reveal, but I will assert that it was done—that is enough. There is no doubt that Fitzsimmons was entitled to the decision and did not foul Sharkey. I got $1,000 for my part in the affair."
And, oh yeah... On December 4, Wyatt Earp went to court on a charge of carrying a concealed firearm. (That Colt he had under his coat when he entered the ring.) He told the judge that he always carried a gun because he usually had cash on him, and because he never knew when he would run into somebody he had put in prison. The judge fined him $50.