"Fifty Grand" was first published in the Atlantic Monthly in July 1927 and later the same year in Men Without Women. It is about the collusive world of gambling and the humanity/compromising of aging boxing champ Jack Brennan during his last fight with Jim Walcott. The fight is likely based on the Jack Britton/Mickey Walker fight in Madison Square Garden on November 1, 1922, although Carlos Baker (author of Hemingway: A Life Story) asserts it was the fight between Britton and Benny Leonard on June 26, 1922, at the New York Hippodrome. Recently, omitted pages from original drafts of the story indicate that the Leonard fight was referred to in retrospect, making it a near certainty that the Britton/Walker fight is the basis for the Brennan/Walcott fight in the story. It is also likely that the foul and "double-cross" was inspired by the Siki/Carpentier fight in Paris on September 4, 1922.
The aging hero, a common figure in Hemingway's work, is Jack Brennan, aged 37, trained by Jerry Doyle, the narrator, at Hogan's health ranch. Dwelling on his age, his insomnia and how much he misses his wife, Jack decides this will be his last fight. The day before the fight, he is visited by his manager, John, and two strangers—Steinfelt and Morgan, referred to as "wise boys" and "sharpshooters." John asks Jerry to leave the room, so the reader does not know for sure what John, Steinfelt and Morgan, and Jack talk about. After the meeting, Jack gets drunk and tells Jerry that he is going to bet $50,000 against himself. Jack says that since he knows he cannot win against a younger, stronger fighter, he may as well make some money on the deal: losing intentionally will be easy. He tells Jerry to bet on Walcott. Most initial interpretations of this secret meeting assume that Steinfelt and Morgan conspire with John to bribe Jack to fix the fight. Following this interpretation, Jack makes a good showing and almost loses his bet when Walcott throws him a low blow. Walcott would have been disqualified, making Jack the winner of the fight and loser of his bet. (This is the double-cross" John later refers to: Walcott's low blow might be evidence that Walcott intended to fix the fight.) Jack stays on his feet to save his bet, inevitably loses the bout, and saves some integrity by making it to the final round. John apologizes for asking Jack to lose intentionally.
There is another interpretation. James Tackach's article "Whose Fix Is It Anyway?: A Closer Look at Hemingway's 'Fifty Grand,'" states that Jack never decided to throw the fight (until the last round). Either Steinfelt and Morgan offered to pay Jack to lose intentionally and he refused; or, Jack had his manager summon Steinfelt and Morgan (as bookies), so that Jack could place his $50,000 bet. If this interpretation is correct, Jack genuinely tried his best but was absolutely sure he would not win, so decided to bet on Walcott and make some money. Jack controls the beginning of the fight, eventually tires (as he, Jerry, and John seem to have anticipated), and Walcott takes over. Walcott hits Jack below the belt, Jack survives, then fouls Walcott and is disqualified. John apologizes because Jack is so beaten and it is the end of his career.
In either scenario, Jack is not simply in this for monetary reasons. He gives a good fight by going the distance and struggling through Walcott's foul (which may or may not have been evidence of Walcott's own fix). Jack's foul is probably intentional. In any case, by fouling Walcott in the last round, Jack does eventually cause his own defeat.