ConceptCalls interrupt turn order.
Normally, play moves around the table in order. Calls interrupt that order.
If South discards and North calls, North exposes the set and then discards. North discards because the tiles in North’s exposed melds and concealed hand should tally to 13 until North has a winning hand.
Visual exampleEastWaiting
SouthDiscarded
WestWaiting
NorthCalled
Call interrupts order
South discards
North discards
After exposing the meld, North discards so North’s concealed hand plus exposed melds tallies to 13 tiles until a winning hand.
Rule in plain EnglishCaller discards next.
South discards, North calls, North exposes the meld, then North discards.
TakeawayCalls interrupt turn order and move play to the caller.
The caller exposes the set, then discards to return to the normal tile count.