The basic thought in Ultimate seems to be that zone defense is effective versus bad teams, or when it's windy. Traditionally the purpose of the zone is to force the offense to make a bunch of passes and hope the wind or poor skills cause a turnover. This is even more apparent when you look at the current movement in zone offenses to forsake the repeated swings for fewer yet higher risk passes downfield.
This means that when you're playing a solid team, and it's not windy, you can't play zone. Well, you can't play the traditional style of zone. My theory of zone play is a little different from that outlined above. I think zone can be played at anytime, against any team. The two keys to zone being effective in these situations are aggressiveness and deceptiveness.
Aggressive zone play is fairly straightforward. Instead of waiting for the offense to turn it over themselves, or for the wind to force a turnover, the defense looks to gamble and create turnovers. This doesn’t mean that every position should look to gamble. It is often more effective for only one position to be allowed to gamble. The player at the gambling position will be able to rely on the other positions acting in an expected manner in various situations.
One example of this is allowing your short deep to gamble. The short deep knows what to expect out of the cup’s play, and can gamble on swings. The short deep will also need to know what the wings are doing, and the wings will have to be able to help cover for the short deep when he/she moves out of position.
Another example is allowing your markers to take chances. This can be particularly effective if you have intimidating marks. By knowing that the ‘back side’ of the defense is going to help contain the disc if a mark gets broken, it gives the mark the ability to try for a handblock or deny the dump, etc.
It is also helpful to build zones around a gambling position. If you have gambling marks, you need to make sure the ‘back side’ defenders are positioned so as to contain the disc even if the marker gets broken. Or perhaps you set up the entire zone so that there is no assumed force side at all. If your short deep is going to gamble, you need to make sure you have wings positioned to take up the slack in the middle of the field. Many of my zones rely heavily on one deep deep being able to cover a large amount of the field. This requires the ‘front side’ of the defense to prevent easy deep throws, particularly to the side away from the disc.
It is important to realize that in a gambling defense, you may get burned. If the opponent gets an easy score now and then, that is to be expected. The ability to actually create turnovers can sometimes be worth the risk of giving up quick and easy scores.
One last comment on aggressive play: Any gambling player should try not to make the same gambles every time, as the offense will quickly learn to take advantage. This leads us to Part 2 which will cover deceptive zone play.