Rules for Tenpai Race

Invented by Nobuyuki Fukumoto in his famous manga Ten: Nice Guy on the Path of Tenhou, this style of mahjong is possibly the best test of reading your opponent's discards. Each hand in this game is made up of two distinct phases: Stage A (the hand building phase), and Stage B (tenpai deduction phase).

The game begins identically to normal Japanese Riichi style mahjong. The two players together shuffle the tiles and build four walls, roll the dice to separate the dead wall and draw their starting hands, etc. The only difference at this point is that both players only start with 10,000 points instead of 25,000.

STAGE A

Each hand begins in Stage A. Stage A follows the same basic rules as regular Japanese Riichi style mahjong: Each player takes turns drawing and discarding tiles as they build their hands. The only real difference is that a player may not declare a win during Stage A (neither by using the opponent's discarded tile, nor by drawing the winning tile yourself). You may still make an open chii, pon, or kan using the opponent's discards. If both players discard 18 tiles, the hand is considered a draw. During a draw, neither player reveals their hand, no non-waiting penalty is paid, the winds do not shift, but one repeat counter is still added to the table.

STAGE B

Any time immediately after discarding, a player may start Stage B of the game if the following conditions are met:

• That player is in tenpai (i.e., able to win immediately if one specific tile is drawn).
• That player is not in furiten.

Note that a player cannot declare riichi if they are in furiten, and they must start Stage B immediately if they declare riichi. Additionally, a player is not forced to start Stage B as soon as they are in tenpai if they do not wish to.

The player who starts Stage B is now the 'attacker' and the opponent is now the 'defender'.

The defender now selects any two tiles from a spare mahjong set and reveals them to the attacker (if no spare mahjong set is available, the defender can simply name two tiles aloud). If the attacker is waiting on either of those two tiles, he must reveal his hand to the defender. The hand then ends in a draw, a repeat counter is added to the table, and a new hand is started, but the winds do not shift.

If neither of the two selected tiles are the attacker's waits, the attacker gets to draw the next five tiles, one by one, revealing any that are not his winning tile. The attacker may not change his hand at this point: He must reveal any tile that does not complete his hand. If the attacker draws his own winning tile, he reveals his hand to the defender and wins.

If he does not draw his winning tile, the defender selects another two tiles that he thinks the attacker is waiting on. This continues until the defender successfully guesses the attacker's wait, the attacker draws his winning tile, or only the 14 tiles of the dead wall remain.

If the attacker draws a tile he can use to make a closed kan or promoted kan, he is allowed to do so: A replacement tile is drawn from the dead wall and a new kan dora is flipped as usual. If the attacker draws a tile that he could use to win, but he does not want to do so (e.g., he is waiting on either 2 or 5, but the 2 is the dora and therefore worth more points), he may elect not to win off of that tile. If he does so, he places that tile face down instead of revealing it, and tell the defender that he is choosing not to win off of that tile. If he later draws another copy of that same tile, he may still choose to win off of it this time.

The winds do not change unless the non-dealer draws his own winning tile while in Stage B. When this happens, all repeat counters are removed from the table.

SCORING RULES FOR TENPAI RACE

No points are exchanged if the hand ends in a draw, or if the defender successfully guesses the opponent's wait. If the attacker wins, he collects all of the riichi bets current on the table and scores his hand as if he won off of an opponent's discarded tile. Instead of collecting those points from the opponent, he simply adds that many points to his score from a central pot. As such, a player cannot lose points, except by declaring riichi. For this reason, the dealer will always earn more points on a win than the non-dealer would, and there is no downside to being the dealer.

Because of the rules of the game, a player cannot score the yaku 'Rob a Kan', 'Last Tile Discard', 'Gift of Man', 'Gift of Heaven', or 'Gift of Earth'. By convention, both 'Eight Dealer Keeps' and 'Pool of Dreams' cannot be scored.

The first player to have 50,000 points is the winner.