A Basic Example

In 3 NT, spade leads and West's two aces hold declarer to seven tricks.

In 5 ♣, the defense gets a club, a heart, and a diamond.

Can 4 ♥ make? If the defense tries to force declarer to lose control, by leading spades, declarer wins the ♠ Q on the first round, leads trumps until West wins, and wins a second spade. Declarer draws a third round of trumps, leaving East with a trump, then leads a diamond. West should duck, declarer wins the ♦ Q, then ducks a diamond to West. West can now force declarer to ruff a spade at this position:

What should East pitch? If East pitches a club, declarer ruffs, cashes two clubs and leads the diamond off dummy, finessing with the ♦ 10. East gets the last trick with the outstanding trump.

If, instead, East ruffs the spade, South overruffs and only has a club loser remaining, again taking the diamond finesse.

So, East must pitch a diamond, leading to this position:

Declarer now plays two top diamonds. If East ruffs, he is forced to lead from his clubs, while if East pitches a club, East only gets his trump trick at the end.

Any defense which does not force in spades will allow declarer to lose just the two red aces and a club.

The five-card end position above is quite common in 4-2 fits in the collection. It's an odd sort of trump strip-squeeze, almost. East is endplayed if he ruffs, but he loses his "natural" club trick if he pitches a club.