What is mahjong fraud? Better give an example. Thank you!

Mahjong cheating refers to the behavior that one party claims to win the game by illegal means, which is against the rules. For example, suppose three people are playing mahjong. A, b, c, a and b already have some cards. C's hands are: 1. 1 00000,10000,10000, 50000, 60000, 70000, 80000, sliver 2, sliver 3, east wind, west wind, south wind. C declares "heaven and earth". After investigation, it was found that C had already played 10,000 cards, so the game continued normally.