In the play of the cards one must follow suit if able to do so, and a failure is an infringement of the laws, and is called a revoke. The emphasis is on preventing this happening, so as defender you can ask partner “having none”, and likewise dummy can ask declarer. So if you discover that you could have followed suit, then you are able to correct the position without penalty. Once play has commenced to the next trick, the revoke is established. Of course many revokes are not discovered until much later in the play (dummy may not point out a revoke by defenders). At that point always call the Tournament Director. One thing you cannot do is just replace the cards at the point when the revoke occurred..

The TD will ask what happened on the trick when the revoke occurred. In particular whether the offending side won the revoke trick. In addition he will inquire whether any tricks subsequent to the revoke trick were won or will be won by the offending side.

If the offenders win the revoke trick, then one trick is transferred to he other side. Should the offenders win any trick subsequent to the revoke trick then one further trick is transferred. Popular opinion say that two tricks are given to the other side but this is not true, it can be zero, one or two. If declarer revokes (quite common!) but dummy wins the trick, there is no penalty for that trick, but may be for subsequent tricks. Dummy can revoke (very rare), but there is no automatic penalty. A second revoke in the same suit does not bring a further penalty.

Should a revoke deny access to established winners (often on dummy but can be in defender’s hands), then the TD can restore equity and transfer more than two tricks from the offending side.

There is no revoke after the eleventh trick is completed, but the offender’s partner may be restricted if he has a choice of cards.

It can be complicated to assess any penalty when a revoke is discovered, so always call for the TD.