Casinos operate under a myriad of rules from both state and federal governments. They are one of the most regulated businesses in the US. Sometimes, when all those regulations aren't met, the casino may refuse to pay you, at least momentarily.
The most common type of casino crime is known as cheating and swindling. A person who purposely or knowingly commits fraud while attempting to win money at the casino can be charged with a criminal offense for cheating and swindling.