Source: Mr. Bridge
Often the best way to play a suit is not to play it yourself but to let the other side lead it. With A-J-x facing K-10-x you have a two-way guess — but not if the opponents lead it. If you play on a suit like Q-x-x facing J-x-x, you will need to find a helpful layout, such as the A-K in one hand for you to set up a trick. However, you are sure of a trick if the opponents lead it. Likewise, if you have an A-Q holding, you are sure of a second trick if LHO leads the suit. Of course, defenders are wise to this. They lead these suits only when you have taken away their other options.
You are South in 4.
West leads the heart jack, which you win with the ace. You cash the ace of trumps and are pleased to see all follow. If you play on diamonds yourself, you will be out of luck because West has the ten and nothing else nice happens. How do you make someone else lead the suit? You do not give up your trump loser yet. The opponents can still lead hearts or clubs safely. First, cash your other heart winner and play three rounds of clubs (you do not mind if someone ruffs a club — it will be with the master trump). Now that you have stripped the side suits, the stage is set. You give up a trump, not caring who wins:
If whoever wins the trump (here East) leads a heart or club, you ruff in one hand and discard a losing diamond from the other (a ‘ruff and discard’). If instead, a diamond comes back, you can be sure of a trick in the suit. Sometimes you need to do more than cash winners to stop your opponents from having a safe means of getting off play. This you will see on the next deal. Another feature is that you may be able to throw someone in with the suit that you want back. If you have a double finesse suit, say A-J-10 facing low cards, you can make an extra trick even if the missing honours are offside. To achieve this you strip the other suits before you take the finesse.
You are in 6 now. West leads a heart. You win and draw trumps. Again, you want to strip the hearts and clubs. Play four rounds of clubs; throw a diamond on the third round and ruff the fourth when East follows. Finally, you ruff a heart in dummy to leave this position:
You finesse the nine of diamonds (or cover the jack with the queen). West wins but has no safe exit. A heart would give a ruff and discard while a diamond goes into the tenace. Note the normal features of a throw-in (or elimination play or endplay):
1 You need a suit or suits that you want the opponents to lead.
2 You need to play other suits either so that the opponents have run out or so that you and dummy are both void —this way, if they can play some other suit, it gives you a ruff and discard.
3 You give up your loser.
The normal things to look for if you want to try for a throw-in are:
1 Enough trumps so that you will have at least one trump left in each hand after you draw trumps.
2 A suit you want someone else to lead — a guess suit such as K-10-x facing Q-9-x, a frozen suit like A-10-x facing K-9-x or, if you can choose which defender leads, a tenace suit.