In contract bridge, avoidance play is a play technique whereby declarer prevents a particular defender from winning the trick, so as to eschew a dangerous lead from that hand. The dangerous hand is usually the one who is able to finesse through declarer's honors, to give a ruff to the partner or to cash one or more established winners. Avoidance play can be regarded as one type of safety play.
|♠||A J 9 6|
|♥||7 5 2|
|♣||A Q J 10 2|
|♠||K 10 8 4|
|♥||Q 8 4|
|♦||A 9 6 5|
South plays 4♠ and West leads ♥K (indicating the ace), East playing the 3 (signalling the odd number of hearts and discouraging the continuation). West continues with a club, increasing the probability of defensive ruff in that suit.
The declarer has plenty of tricks, but is missing the trump queen and two top hearts; giving up the third heart early would probably mean losing the contract. Since ♥A is almost certainly with West, if East gets the trump queen, he could finesse declarer's ♥Q. Thus, the declarer must not allow East to get the trick, and so must play a trump first and finesse against the queen in East's hand. If West has the ♠Q and takes it, he could only take one more heart trick.
Note that, even if South had fifth trump instead of a diamond (playing in 5-4 fit), the same technique - finessing the queen against East - would practically ensure the contract (safety play). If the trumps are distributed x - Qxx, the percentage play of playing AK in trumps would endanger the contract, as East could ruff a later round of clubs with ♠Q and play a heart through. With the avoidance finesse, West could win a "non-existing" trump trick if the trumps were distributed Qx-xx, but could not set the contract.