Ron (ロン) is a win completed on a tile discarded by another player rather than one you draw yourself. To call ron you must already be in tenpai, hold at least one yaku, and the discarded tile must complete your wait. It is the opposite of tsumo, the self-drawn win.
When an opponent discards a tile that finishes your hand into the kawa, you declare 'ron' before the next draw, reveal your hand, and score it. Outside pao liability on certain yakuman, the discarder pays the entire hand alone, unlike a tsumo shared among all three opponents. A standard closed hand won by ron also receives 10 fu of menzen kafu; chiitoitsu stays fixed at 25 fu and yakuman do not use fu.
Furiten blocks every ron if any tile in your wait appears in your own discards. Under Tenhou rules, two players may win on the same discard, while three simultaneous ron calls cause an abortive draw. WRC 2025 pays only one winner: the player closest to the discarder in turn order, regardless of declaration speed.