We've prepared the absolute requirement for betaori. For the next 2 to 3 articles, we'll be explaining how to betaori using actual games.
This article will be explaining when we should go into betaori. (To a certain degree, this is a discussion about offence and defence for beginners.) Look at the game below.
[First image in http://blog.jpmahjong.net/read.php/542.htm]
Kamicha declared riichi at the fifth discard, what should you do?
Discard west here, just for this discard. Someone who discards anything else, might not have the qualifications to discard on the level of "Special". (Translator note: My guess is that the author is referring to a ranking called "Special".)
The hand is currently in yonshanteen, while kamicha is in tenpai, the situation is like you're 50m behind someone in a 100m race, don't even think of trying to catch up. Additionally, avoiding a deal-in while trying to reach tenpai is a difficult problem.
Betaori is the only way for this sort of tiles.
[Oh, let's discard 1 pin and see what's going to happen next.] Thoughts like this, should be avoided at all cost. You must discard the safest tile, xia here.
Remember, when in betaori, start with the safest tile.
Usually, if you want to pursue riichi or challenge someone in tenpai, you need to have a iishanten or better with a good shape. For anything ryanshanten or below, unless there are no safe tiles or the situation is special, please do not hesitate going into betaori.
In Japan, some high quality tactics discussion recommend beginners to employ a simple offence and defence baseline.
Once an opponent declares riichi, if your hand is already in tenpai, then attack immediately(or pursue riichi), or else go into betaori.
Do not underestimate this method of judgement, if everyone can execute this perfectly, going up to 3 dan, or even entering "special" might not be a problem.
Shanten number, is more important than hand value
The largest factor in deciding whether or not to attack, is your own shanten number, instead the hand value is a secondary factor. Because, if you win, your opponent's chance of win disappears at the same time. A hand worth 3900 points in tenpai, is better to attack with than an iishanten hand worth 8000 points.
[Second image in http://blog.jpmahjong.net/read.php/542.htm]
The hand in the image above has a high chance of becoming a mentanpin dora 1 mangan hand. But if shimocha declares riichi, and your hand is still in ryanshanten, you should immediately go into betaori.
In this discard, discarding the live tiles xia or haku is very dangerous. You should discard the two genbutsu, and go into betaori. Most beginners find that it's very unnatural to go into betaori here, but having the courage to go into betaori with such good tiles, is an important step to improving.