Question: What was the unofficial name of the event that caused the man who defeated the great John L. Sullivan to rescind his retirement after hearing of the outcome?

Context paragraphs:
USAT John L. Clem: John L. Clem began her service life as the United States Navy troop transport USS "Santa Ana" (ID-2869).  Between the wars she served as a commercial ocean liner under various names.  In 1941 she was acquired by the U.S. Army and assigned the name USAT "John L. Clem, about which time she was also briefly assigned a US Navy ID, AP-36.  She did not serve with the navy however, and spent most of the war as an army transport until being converted into a hospital ship, the USAHS "John L. Clem.

Mrs. John L. Strong: Mrs. John L. Strong is a privately held American luxury company and manufacturer of custom papers and stationery.  Founded in 1929 by Mrs. John L. (Flora) Strong, the company has created papers and custom luxury products for seven presidential families, royal houses, prominent members of international society, film stars and celebrities.  Called the ""ne plus ultra" of chic stationery companies," Mrs. John L. Strong has an important international clientele.

Catch and release (U.S. immigration policy): Catch and release is the unofficial name for a protocol historically followed by immigration enforcement agencies in the United States (specifically, by U.S. Immigration and Customs Enforcement and U.S. Customs and Border Protection) where people caught for being in unlawful immigration status are released while they wait for a hearing with an immigration judge.  The policy officially ended in 2006 under President George W. Bush and United States Department of Homeland Security Secretary Michael Chertoff, where it was replaced by a "catch and return" or "catch and detain" policy.  However, some critics of immigration enforcement in subsequent years, particularly under the presidency of Barack Obama, have dubbed various policies and practices under the administration as catch-and-release policies.

Hamza River: The Hamza River (Portuguese: "Rio Hamza") is an unofficial name for what seems to be a slowly flowing aquifer in Brazil, approximately 6000 km long at a depth of nearly 4000 m .  Its discovery was announced in 2011 at a meeting of the Brazilian Geophysical Society in Rio de Janeiro. <ref name="Hamza Google/AFP"> </ref> The unofficial name is in honour of scientist Valiya Mannathal Hamza, of Brazil's National Observatory, who has undertaken research on the region for four decades.  The Hamza "river" and the Amazon River form a geologically unusual instance of a twin-river system flowing at different levels of the earth's crust.

Caleb S. Denny: Caleb Stone Denny (May 13, 1850, Monroe County, Indiana – March 24, 1926) was the 15th and 17th mayor of the city of Indianapolis, Indiana.  Denny first worked as a teacher and librarian before completing a law degree.  He served as the assistant attorney general of Indiana from 1873 to 1875.  In 1885, Denny resigned his position of city attorney to try to obtain the Republican nomination for mayor of Indianapolis.  He ran successfully against incumbent mayor John L. McMaster and won the subsequent election by only 60 votes (out of approximately 18,000).  Denny was reelected in 1887.  He chose not to run in 1889 and Democrat Thomas L. Sullivan was elected as mayor.  In 1892, Denny returned to politics and defeated Sullivan.  He served a single term.

James J. Corbett: James John "Gentleman Jim" Corbett (September 1, 1866 – February 18, 1933) was an American professional boxer and a former World Heavyweight Champion, best known as the man who defeated the great John L. Sullivan.  Despite a career spanning only 20 bouts, Corbett faced the best competition his era had to offer; squaring off with a total of 9 fighters who would later be enshrined alongside him in the International Boxing Hall of Fame.

Dan Dobbins Peak: Dan Dobbins Peak is the unofficial name given to the officially unnamed highest mountain in the Jackson Mountains of Humboldt County in Nevada, United States.  It is the most topographically prominent peak in Humboldt County and ranks tenth among the most topographically prominent peaks in Nevada.  The peak is on public land administered by the Bureau of Land Management and thus has no access restrictions.  The unofficial name noted in the summit registry book is said to refer to a hiker who died on the peak.

The Great John L.: The Great John L. is a 1945 American biographical drama film directed by Frank Tuttle and written by James Edward Grant.  The film stars Linda Darnell, Barbara Britton, Greg McClure, Otto Kruger, Wallace Ford and George Mathews.  The film was released on May 25, 1945, by United Artists.

Fitzsimmons-Maher Prizefight: The Fitzsimmons-Maher Prizefight (February 21, 1896), also considered, unofficially, as the 1896 World Heavyweight Championship, occurred between Bob Fitzsimmons and Peter Maher on a sandbar in the Rio Grande River just far enough outside of the American city of Langtry, Texas, in which state boxing was illegal, to be considered technically in the Mexican state of Coahuila de Zaragoza.  Fitzsimmons was victorious, knocking Maher out in the first round; however, upon hearing of the outcome of the fight, the 1895 World Heavyweight Champion James J. Corbett immediately rescinded his retirement.

Fall 2012 Tour (Kansas): The Fall 2012 Tour (unofficial name) is a concert tour by the American progressive rock band Kansas.  Each concert featured King's X as the opening act.  The tour featured several songs not played live by the band in several years, including "Paradox," "Can I Tell You," and "Journey from Mariabronn," as well as a short medley of songs from "The Ed Sullivan Show" (classified as "Ed Sullivan Medley").  A backdrop of the album cover of the band's first album (which is a cropped photo of the "Tragic Prelude" painting) was also featured on the tour.

Supporting paragraphs: Fitzsimmons-Maher Prizefight James J. Corbett
Answer: 1896 World Heavyweight Championship