You’re referring to heavyweight champion “Gentleman Jim” Corbett, rather than John L. Sullivan, and Horn did not have a run-in with the boxer. However, the screenwriters may have borrowed from a true incident.
While perusing my 1977 history of Arizona, I ran across a story about Sullivan visiting Tombstone in 1884 to put on an exhibition of fisticuffs. He offered to pay anyone who could stay in the ring with him for two rounds. One of the challengers was Jim Younger, a black cowboy working for rancher John Slaughter. Younger staggered the champion with a roundhouse blow in the first round, but the pugilist recovered and won the fight.
At the time of the champion’s trip, the five men convicted in the so-called Bisbee Massacre were awaiting the hangman’s noose in the Tombstone jail. Sullivan paid them a visit.
Dan Dowd admonished his fellow Irishman: “John Sullivan, you think you are a great man because you can knock out one man in five rounds, but our sheriff here, who is much smaller than you, can knock out five men in one round.”
Marshall Trimble is Arizona’s official historian. His latest book is Wyatt Earp: Showdown at Tombstone. If you have a question, write: Ask the Marshall, P.O. Box 8008, Cave Creek, AZ 85327 or e-mail him at firstname.lastname@example.org