The main basis for why Stu switched from gin rummy to poker was that Stu was a little too skilled at it. So skilled was he, that no one could equal him. Even the commonly called professionals who were meant to be the best at gin rummy were beat when they played with Stu Ungar. One such gin rummy masters was Harry Stein, nicknamed, "Yonkie". Mr. Stein suffered such a crushing beating at the hands of Stu Ungar that he evidently quit playing it as a pro and never resurfaced at a gin rummy tournament.
Certainly, with a honor like that it was not very long before people became afraid of playing against mr. ungar. He could not find any matches and in his boredom he began doing something no one had performed before. Stu issued beginning handicaps to potential adversaries with the hope that they might compete against him if they believed they had an advantage. He at will played from a disadvantageous position and one story has it that stu even played against a consistent bad egg. During the game, he get advice that the absconder was at it yet again but stu guaranteed that he was aware of the chicanery and he would still acquire a win, which of course, he did.
The same problem followed Stu Ungar into Las Vegas. He won so much that the casinos began requesting that he not to wager on their rooms anymore. The reason for it was that other poker room clients would not sit at the table if Stu was seated.
Stu Ungar is recalled more for his accomplishments in holdem poker but he always said that he was far more skilled at gin rummy.
He defeated Doyle Brunson in the WSOP in 1980 and became the youngest world champion. Because of his looks that made him seem far younger than he was, he got the nickname, "The Kid".