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By Tom Sloper
4th of July, 2010

Column #458

American Mah Jongg (NMJL rules). As I wrote on the Q&A bulletin board this week, the Window of Opportunity rule is probably the single most important rule in American mah jongg. The moment when a player is claiming a discard for exposure is a moment of excitement; taking the tile is a forward step towards the goal: making mah jongg. Even more exciting is the moment in which one obtains the tile that completes the hand, triumphantly taking the player over the mah jongg finish line.

If something happens at these moments of excitement to thwart either the step closer to victory, or the step over that finish line, it frequently happens that the player snaps; thwarted elation can often turn to anger. So it's very important that the rules governing this crucial window of time are clearly understood by all players. The unfortunate fact is that most players have never even seen the complete actual rule in writing. Most players learned what they know about the rule by word of mouth, and usually what they heard was incomplete or incorrect.

When a discard goes down (when the tile either touches the table or is named completely), the window opens. While the window of opportunity is open, any of the other three players can claim the live discard. The window doesn't close until one of the following three things occurs:

1. The next player picks and racks;
2. The next player picks and discards;
3. The next player picks and declares mah jongg.

The window of opportunity doesnít close, then, when the player next in order lifts the next tile from the wall (or slides it, which is essentially the same thing), or when she looks at the tile (as many people seem to think); it doesn't close until she racks or discards or declares mah jongg. Once any of those three things happens, no player can call the most recent discard, because that discarded tile is now dead.

If a player wants to claim the live discard within the window of opportunity, she may do so. When a claim is spoken, if the next player in line was holding a picked tile, or looking at it, or moving it towards her rack, she has to put it back on the wall. It sometimes comes down to a judgment call; was the first syllable of the claim audible before the click of the tile on the rack, or not? If the call and the click were concurrent, I consider the length of the interval between discard and claim. If the claimant had been slow to make the claim, then the picker keeps her tile; if the picker had moved rapidly (making it difficult for another player to make a claim), then the claimant gets the discard.

Where this gets tricky is when the picked wall tile is the picker's maj tile. A claim for maj trumps a claim for exposure. Similarly, if someone voices a claim for the live discard while the picker sees that the tile she's taken is her maj tile, then she doesn't have to put that tile back on the wall; she gets to declare maj. Mah jongg trumps everything. It's only right.

Don't stop reading here! Some readers wrote in with follow-up questions in 2014 and 2016 (below). And this topic was discussed again in column 639 in July, 2015.

Question or comment about this column? I often miss something; maybe you'll be the first one to spot it! Please be gentle. Email and the discussion will be posted on the Mah-Jongg Q&A Bulletin Board.

Where to order the yearly NMJL card: Read FAQ 7i.

Need rules for American mah-jongg? Tom Sloper's book, The Red Dragon & The West Wind, is the most comprehensive book in existence about the American game. AND see FAQ 19 for fine points of the American rules (and commonly misunderstood rules). AND get the official rulebook from the NMJL (see FAQ 3). Linda Fisher's website is the only website that describes American rules:

© 2010 Tom Sloper. All rights reserved.