"To welsh" is also a
slang phrase meaning to refuse to pay one's debts or obligations. Two spellings, welsh or
welch, exist though the original spelling of the word is welsh.
The origin of the use of the phrase extends back to the eighteenth and nineteenth centuries around race tracks in England for people who would not make good on their bets. The origin of the phrase as been attributed to two sources, neither of which are directly connected to the the Welsh people. The first is that it was English bookies who were not paying their debts and who would flee to Wales in an attempt to avoid prosecution, causing the adoption of them having "welshed" on their bets. The other tale of the origin of this phrase is that one particular English bookie, a man named Bob Welch, was the culprit in this scenario and it was the similarity between his name and that of the natives of Wales that caused the use of the phrase.
It should be noted that Welsh societies in the U.K. and in the U.S. have been trying to have the phrase expunged from popular use, which may have led to the increase in the use of the alternate spelling and pronounciation of "welch."