Winning on a discard
If another player discards the tile that completes your hand, call out immediately — "Mahjong!", "Hu!" or "Ron!" — and take the tile. A win claim takes priority over any other claim. If two players claim the same discard for a win, rule sets differ: some give it to the player next in turn order, others allow multiple winners.
Lay your full hand face up so everyone can check it. The discarder typically pays the most, and in Hong Kong and Japanese play often pays the whole amount.
Winning by self-draw
If the tile that completes your hand is one you drew from the wall, you win by self-draw — called zimo in Mandarin, tsumo in Japanese and self-pick in American play. Self-draws usually earn a bonus, and every other player pays.
In Japanese play a fully concealed hand completed by self-draw gains its own scoring element, menzen tsumo.
Checking the hand
Once declared, the winning hand is checked by all players before any tiles are mixed back into the wall. Players confirm that the shape is legal, that the hand meets the minimum value for the style and that scoring elements are counted correctly. Taking a moment here prevents most disputes.
In American play, the winner names the card hand they have completed so others can check it against the card.
False declarations
Declaring a win with an incomplete or invalid hand is a serious error. Depending on the style, the player may have to pay every other player as if they had lost, play on with a dead hand, or the hand may be replayed. Riichi rules call this chombo and impose a fixed penalty.
The habit to build is simple: check the shape once more before you speak, especially when excited.
