what does it mean to welch on a bet
Welsh (surname) A related colloquialism is the verb to welsh/welch ('to renege') as in 'to Welsh/welch on a deal or bet', which may be derived from an age-old 'English' stereotype of the Welsh/Celtic peoples as unreliable oath-breakers, though that etymology remains conjectural.[1] The potential association with a negative stereotype results in it being considered a somewhat pejorative term.
Blackjack At a casino blackjack table, the dealer faces five to seven playing positions from behind a semicircular table. Between one and eight standard 52-card decks are shuffled together. At the beginning of each round, up to three players can place their bets in the "betting box" at each position in play. That is, there could be up to three players at each position at a table in jurisdictions that allow back betting. The player whose bet is at the front of the betting box is deemed to have control over the position, and the dealer will consult the controlling player for playing decisions regarding the hand; the other players of that box are said to "play behind". Any player is usually allowed to control or bet in as many boxes as desired at a single table, but it is prohibited for an individual to play on more than one table at a time or to place multiple bets within a single box. In many U.S. casinos, however, players are limited to playing two or three positions at a table and often only one person is allowed to bet on each position.