Source: Wikipedia Dummy reversal (also known as reverse dummy) is a technique in contract bridge whereby declarer uses trump cards to ruff from the hand with more (longer) trumps, and retains the trumps in the other (shorter) hand to draw the opponents’ remaining trumps. Normally in play technique, ruffs are taken from the hand with shorter trumps, retaining trumps in the longer hand for control. Declarer, being the first to have bid the suit, usually has more trumps than his partner (the eventual dummy) and so the term “dummy reversal” is used to describe the case where during the play, dummy is made to have more. The purpose of dummy reversal is to yield more tricks than the normal technique; the technique can be adapted for use in other trick-taking games.

Indicators:

Some indicators that a hand may lend itself to dummy reversal are:
  • shortness (singleton or void) in declarer’s hand with length in the same suit in dummy
  • loser(s) in declarer’s hand that cannot be ruffed or discarded on a side suit
  • adequate trump strength and length in dummy (typically a three or four card trump suit with at least two honors for drawing the final trumps)
  • entries to dummy outside of the trump suit

Example:

AKJ W             E Q10853
A854 6
AK2 954
A64 J853
      East is in 4and receives a trump lead. There are five trump tricks, three aces and king of diamonds off the top, but there is no tempo to ruff a club in dummy, as the defenders will deprive it of the trumps after they regain the lead in clubs. The solution is to ruff hearts in hand instead – in trick two, East playsA, ruffs a heart, enters the dummy withA, ruffs a heart, enters the dummy withA and ruffs a heart. In this way, the declarer took three ruffs in hand, and still has two trumps in dummy to take care of opponents’ trumps (assuming that they are divided 3-2, which is the most common division of five cards).