Page "Scoring in Mahjong" Paragraph 34

Many variations may also impose penalties for discards that are considered to be " high risk " when the size of the wall is winding down.

If a player wins from a high-risk discard, the player who discards the winning tile often must suffer an additional scoring penalty.

The winner is not usually affected by a high-risk discard, and frequently the other two losing players are " off the hook ".

Typical high-risk scenarios include scenarios where a player is threatening to win with a ( necessarily highly exposed ) high-point hand.