The basic basis for why Mr. Ungar switched from gin rummy to poker was that he was a tiny bit too skilled at it. So skilled in fact, that no one possibly could equal him. Even the so-called champions who were meant to be the greatest at gin rummy were devoured when they played against Stu Ungar. One such gin rummy professionals was Harry Stein, called, "Yonkie". Harry was handed such a humiliating beating at the hands of mr. ungar that he evidently stopped playing it professionally and never resurfaced at a gin rummy tournament.
Accordingly, with a distinction like that it was not very long before everyone became shy of gambling against mr. ungar. He could find no games and in his agony he started doing something no one had attempted before. Stu presented starting handicaps to likely opposing players in the hope that they might play opposed to him if they thought they held an edge. He deliberately started from a disadvantageous position and one account has it that he even competed with a consistent absconder. During the game, he get a few words of wisdom that the bad egg was at it again but stu assured that he knew of the cheating and he would still come away with a win, which he did, of course.
The same problem followed Stu Ungar into sin city. He won so frequently that the casinos began requesting that he not to compete in their rooms anymore. The reasoning behind it was that other casino clientele refused to be seated at the poker table if Stu was seated.
Stu Ungar is remembered better for his accomplishments in holdem poker but he always said that he was a whole lot more skilled at gin rummy.
He beat Doyle Brunson in the WSOP in Nineteen Eighty to become the youngest world champion. Due to his looks that made him seem far younger than he really was, he was nicknamed, "The Kid".