The main basis for why Stu Ungar changed from gin to poker was that he was a bit too good at it. So good was he, that no one could stand up to him. Even the apparently professionals who were supposed to be the most favorable at gin were decimated when they competed against Stu Ungar. One such gin rummy player was Harry Stein, called, "Yonkie". Mr. Stein suffered such a crushing beating at the hands of stu that he apparently quit competing in it professionally and never showed up at a gin rummy tournament.
Accordingly, with a reputation like that it was not too long before players became shy of gambling against Stu Ungar. He could not find any matches and in his bleakness he started doing something no one had performed before. He offered starting handicaps to likely opponents with the hope that they may play with him if they believed they held an edge. He at will played from a negative arrangement and one story has it that he even played against a regular bad egg. During the contest, he received advice that the absconder was at it again but Stu Ungar assured that he was aware of the fraudulent activity and he would still win, which of course, he did.
The same trend followed Stu Ungar into sin city. He won so frequently that the poker rooms started requesting that he not to compete in their rooms anymore. The reason for it was that other poker room visitors would not sit at the table if Stu was seated.
Stu Ungar is remembered better for his accomplishments in texas holdem poker but he always maintained that he was much more accomplished at gin rummy.
He beat Doyle Brunson in the World Series of Poker in Nineteen Eighty to become the youngest world champion. Because of his features that made him seem far younger than he really was, he was nicknamed, "The Kid".