American Mah Jongg is settled between players, not with a bank, and the way a hand ends decides who pays. A win on a discard costs the discarder double; a self-drawn win costs everyone double. So throwing the winning tile is the most expensive thing you can do at the table, and the whole of defence is about not doing it.

What a dead hand pays

A hand is dead when no line on the card can still be completed with it. Two things kill it: an exposure that no remaining line can use, and a tile running out. A pair of north winds is gone once all four norths are visible elsewhere. Groups of three or more survive that, because jokers can cover them; pairs and singles cannot.

A dead hand still pays when someone wins. That is the reason to stop feeding the table the moment you know you cannot win: your only remaining job is to not be the discarder who pays double.

Reading the exposures

Every exposure on another rack narrows that player's possible lines, exactly as it narrows your own. One exposed pung leaves a few sections open; two usually leave one; three nearly always leave one line, and you can read on the card what that line still needs.

Two kongs of dots on one rack, both even: the line is in the 2468 section, and the pair it still needs is a tile you will not throw.

Do this out loud in your head, every hand: "Two kongs of dots, both even, so 2468 in dots; the line needs a pair of somethings and the rest is already showing." Then those somethings are tiles you will not throw.

Counting the visible tiles

There are four of every tile. Count what you can see: the discards, every exposure, your own rack. A tile with three copies visible is safe to throw as a pung tile (nobody can complete a pung with it) but not as a pair tile. A tile with all four visible is safe everywhere.

Three Norths showing between the discards and an exposure. The fourth is safe as a pung tile, since no pung of Norths can be finished, and useless to anyone's pair.

Two habits make this easy:

  • The discards are the record. Nothing is hidden about them. A tile that has been thrown twice and not called is a tile the table does not want.
  • Late in the hand, a fresh tile is a hot tile. A number that has not been seen all hand, thrown after the wall is half gone, is the kind of tile that wins hands. Hold it if you can.

When to switch to defence

The calculation is simple and worth doing every few turns: how many tiles am I from my best line, and how many tiles are left in the wall? Five away with twenty tiles left is not going to happen. At that point stop drawing toward your line and start choosing discards for safety: tiles already seen three or four times, tiles no exposure on the table can use.

Going defensive is not giving up; it is taking the double payment off the table. A wall game costs nothing at all.

Practise it

The report card after every hand at the school grades each discard for the danger it carried, given what was visible when you threw it, so you can see which throws were brave and which were careless.