The basic reason why Stu changed from gin to poker was that Stu was a bit too skilled at it. So good in fact, that no one could equal him. Even the apparently experts who were meant to be the most favorable at gin were decimated when they played against Stu Ungar. One such gin rummy professionals was Harry Stein, called, "Yonkie". Harry Stein suffered such a crushing defeat at the hands of Stu Ungar that he apparently stopped participating in it as a pro and never resurfaced at a gin tournament.
Of course, with a notoriety like that it wasn’t too long before everyone became weary of betting against stu. He could find no games and in his agony he started doing something no one had done before. He presented beginning handicaps to potential opponents in the high hopes that they might just compete opposed to him if they thought they held an edge. He at will started from a bad position and one story has it that he even competed against a consistent cheater. Amid the match, he received a few words of wisdom that the bad egg was at it again but stu assured that he knew of the chicanery and he would still win, which he did, of course.
The same problem followed Stu Ungar into vegas. He won so much that the casinos began requesting that he not to wager on their respective premises anymore. The explanation why was that other casino customers would not be seated at the poker table if he were playing.
Stu Ungar is remembered better for his accomplishments in holdem poker but he himself always said that he was considerably more accomplished at gin rummy.
He defeated Doyle Brunson in the World Series of Poker in 1980 and became the youngest world camp. Because of his looks that made him appear far younger than he really was, he was nicknamed, "The Kid".