He boxed as an exceptional amateur for the Los Angeles Sporting Club, under the instruction of George Blake, a master trainer who recognized Jackie's potential as early as the age of thirteen.

[8] As a young fighter, Fields was told by promoters that his birth name presented "the wrong image" because Jews weren't considered tough, physical guys.

Fields won a gold medal in featherweight boxing at the age of only 16 in the 1924 Summer Olympics in Paris,[18] becoming the youngest boxer to ever receive such an honor.

With only six fights and nine months of professional boxing to his credit, Fields lost badly in a second-round knockout at Olympic Auditorium in Los Angeles.

[19] Fields suffered a rare early career loss to Jewish boxer, and former world featherweight champion Louis "Kid" Kaplan on June 15, 1927, in a ten round points decision at New York's Polo Grounds.

Kaplan's two handed attack was unrelenting, and though the taller Fields scored with straight left jabs and a rapid right cross, they did not come frequently enough to gain a margin in points.

[20] He defeated Jewish boxing great, reigning world junior lightweight champion, Mushy Callahan in a non-title bout on November 22, 1927.

[21] In a rare early-career loss, Fields dropped a ten-round unanimous decision to reigning world lightweight champion Sammy Mandell on February 3, 1928.

The San Francisco Examiner believed Mandell had won by the slightest of margins, but noted that the younger and less experienced Fields easily took the second and tenth rounds with harder punching, though he failed to follow up his advantage.

[5] He defeated Young Jack Thompson before 9,000 fans on March 25, 1929, in a ten round unanimous decision in Chicago for the vacant NBA welterweight title.

California, and the National Boxing Association, but not the powerful New York State Athletic Commission (NYSAC), officially recognized Fields as the champion on April 19, 1929.

[8] Fields defeated black boxer William "Guerilla" Jones, future world "Colored" welterweight champion, on October 21, 1929, in San Francisco before a crowd of 10,000.

[28][29] In a match two months later on December 13, referee Joe O'Connor stopped the bout, complaining that Jones was not giving his "usual exhibition" and ordered the promoter to pay the purses for both fighters.

[31] Fields had defeated Vince Dundee in three previous ten round points decisions in Chicago on October 2, 1929, and in two meetings in Los Angeles on April 17, and February 14, 1928.

Thrown off by his opponent's left hand stance, Fields fell behind in the early rounds and though he came back strongly late in the bout, the referee believed Corbett still held a margin on points.

Fields recovered his form two months later with a fourth round TKO against future welterweight champion Tommy Freeman before 8000 fans in Cleveland.

[32] Before a crowd of 14,000, Fields lost his NBA world welterweight title to Young Jack Thompson on May 9, 1930, in a fifteen round points decision at Detroit's Olympia Stadium.

Fields piled up a points lead in the early rounds, but Thompson came back with jabs and uppercuts in close fighting that badly wore down the reigning champion.

Fields regained the NBA (National Boxing Association) world welterweight championship before an enthusiastic crowd of 11,200, defeating Lou Brouillard in a ten round unanimous decision on January 28, 1932, at Chicago Stadium.

[37] Fields lost his NBA welterweight title on February 22, 1933, against Southpaw Young Corbett III before 15,000 fans in a ten round points decision at Seals Stadium in San Francisco.

[9][10] After he lost much of his real estate investments in the depression, Fields lived for a while in the German town section of Philadelphia and worked from 1935 through the 1940s as a salesman for the Wurlitzer Juke Box company and a beer manufacturer, Hannah and Hogg Distilleries.

[40] While in Los Angeles, he appeared in the movies Battling Bunyan (1924), The Prizefighter and the Lady (1933), Big City (1937) and Heavyweight Championship of the World: Muhammad Ali vs. Floyd Patterson (1965).