Benefits:

• Effective against weaker throwers or people without good evasive skills
  
• More effective in windy, wet or cold weather
  
• Helps the defender in one-on-one defense against a cutter in an open field
  

Costs:

• Once broken it is very vulnerable
  
• The marker allows a relatively free throw to one side of the field.
  
• The marker's ability to react to the thrower is restricted, and he cannot back off to restrict a narrower wedge of the field.
  
• If a single person is not forcing properly it allows the force to be broken easily.
  
• it is inappropriate for a team with handlers who are not athletic (one-on-one players)
  

At the same time, because this defense is so common, most of the work in learning a stack is learning how to beat the force. Thus these two strategies have become linked.

My own feeling is that it is never a good idea to give a good thrower a free throw. Having the marker shading one side allows the thrower a fuller windup to go long with the other throw.

Also, I think any good thrower, in particular any taller good thrower (I am 6'2") should be able to throw through the force. I do not believe it possible to shut off half the field, unless perhaps wind conditions are really bad. And a throw through the force leaves all 5 remaining cutters free by 2 steps upfield. When I hear the defense call "No break!" it just lets me know that there is a good opportunity on the break side, and it is rare that I can't hit it.

There are several situations where a force is effective. One is against a team without the skills to break it. A second is that some people/teams are convinced they cannot break it, and so will not even look against it. (I have played with several otherwise good handlers who have been convinced they could not break a force.) Bad weather conditions effectively lower a thrower's skills, so on a windy or wet day a force gains effectiveness.

The benefits do not come without cost though. One cost is that the marker loses a lot of his freedom and flexibility. He must crowd the thrower, and cannot respond to a movement (fake or real) towards the other side of the field.

A second cost is the danger of breaking the force. This is not to be taken lightly - if all the defenders are taking advantage of their knowledge of the force, a pass through the mark means that all five of the remaining receivers have a couple of steps of freedom in exactly the direction their flow wants to take them. If the offense does not score in this situation it is entirely their own failure.

Still, forcing can be a useful strategy on occasion. It works best on a sideline, especially a downwind sideline, because the field is already restricted in that case. It gives the offense a different defense to deal with, so alternating a force with straight-up marking means the cutters may be confused about what type of cut will work best at what time, and the thrower cannot adapt to the mark. Near the goal line when a single pass can score it can help by limiting the likely area that pass can occur. But it is important that it not be used so much that the offense can react and adjust to it, since that allows its drawbacks to be exploited.