The main reason for why Mr. Ungar changed from gin to poker was that Stu was a tiny bit too good at it. So skilled in fact, that no player possibly could stand up to him. Even the commonly called champions who were meant to be the greatest at gin rummy were crushed when they competed against Stu. One such gin rummy player was Harry Stein, called, "Yonkie". Mr. Stein suffered such a crushing defeat at the hands of stu that he apparently quit participating in it professionally and never resurfaced at a gin rummy tournament.
Certainly, with a reputation like that it wasn’t very long before everyone became weary of gambling against stu. He could not find any games and in his desperation he began doing something no one had done before. Stu provided beginning handicaps to likely opponents with the high hopes that they might just compete against him if they believed they held an advantage. He deliberately played from a disadvantageous position and one account has it that he even played against a constant absconder. Mid game, he received warnings that the absconder was at it one more time but stu stated that he knew of the cheating and he would still win, which of course, he did.
The same problem followed Stu Ungar to sin city. He won so often that the casinos began asking him not to play on their poker rooms anymore. The reason for it was that other poker room visitors would not sit at the poker table if he were seated.
Stu Ungar is recollected more for his accomplishments in texas holdem poker but he always insisted that he was a whole lot more accomplished at gin rummy.
He defeated Doyle Brunson in the WSOP in 1980 and became the youngest world champion. Due to his looks that made him appear far younger than he really was, he was nicknamed, "The Kid".