Betaori 「ベタ降り」 is a general strategy emphasizing the discarding of safe tiles or minimizing the chances of dealing into other player's hands. By employing betaori, a player has abandoned the prospect developing a completed hand; and instead, the player opts to minimally lose points via opponent tsumo or ryuukyoku. Of course, a player in betaori hopes to not lose points at all.
Determining safe tiles
The central idea behind betaori involves avoiding dealing into player hands. This requires deduction from visible tiles. The visible tiles are all tiles revealed from the player perspective. This include all discards, the dora indicator, and the tiles in the player's own hand. Of course, tile defense also requires the player's active decision to defend as opposed to continuing to push the hand towards tenpai. Tenpai is still very much possible in this process.
Genbutsu and furiten
Genbutsu 「現物」 is a term for "safe tile" due to furiten, by reading the discard pile. To identify safe tile, players rely on the furiten rule. Furiten refers to a player's inability to declare ron, if any winning tile is within the player's own discard pile. Therefore, discarding tiles applied by the furiten rule are the safest tiles to discard, against particular players.
The most obvious tiles to discard safely are the one in particular opponent's discard piles. However, often, a player may possess a set of tiles in the hand, that are not clearly safe. In this case, a player may have to rely on suji and/or kabe to make an educated guess on a safe discard.
The safest tile to discard is the identical tile discarded by the previous player. This is known as awaseuchi 「合わせ打ち」. Naturally, it is safe against the previous discarder. Temporary furiten renders it safe against the player to the right and the player across.
Ideally, players best seek to use mawashiuchi 「回し打ち」. While trying to play safely, it is best to still not abandon the prospect of forming a hand. After all, a player may terminate threatening hands by outright winning the hand. This practice is best performed, if and only if, the tiles bring about the possibility of attaining tenpai, while not discarding winning tiles.
- Written work on defense in Osamuko