Two different questions sit behind this search. The first is a bet on a game in a pub or club. In Great Britain a bet made by someone acting outside any business is not an offence under the Gambling Act 2005 (section 296), so two friends playing for a stake are within the law; an organiser who takes a cut is in a different position. Other countries and US states have their own rules on private wagers.
The second is online play. Skill-game apps offer cash pool matches as contests of skill and switch cash play off where they judge it is not allowed. Those lists come from the operators, and they do not match. Skillz's terms bar cash competitions in five states: Arkansas, Connecticut, Delaware, Louisiana and South Dakota. The Pool Payday App Store listing names twelve where its cash tournaments are off: Arizona, Arkansas, Connecticut, Delaware, Illinois, Indiana, Louisiana, Maine, Montana, South Carolina, South Dakota and Tennessee. If your state is on either list, expect no cash play in Pool Payday.
In India, the Promotion and Regulation of Online Gaming Act 2025 bans online money games, skill-based or not, from 1 May 2026, and Skillz lists India as not cash-enabled. The P2P gambling laws guide covers other countries.