In the picture above, we see the front half of the stack. The disc has just been thrown from the thrower (top left corner person in red). Let's assume that the disc is still in the hands of the dude in the top left, and talk about the Stack. What is the Stack? The stack is a formation that the offense arrays itself into when it has the disc. There are other formations possible (European, zone offense), but the Stack is the MOST common. In the example above, the player with the disc (Red Team) is in the top left corner. He is not technically part of the stack. The rest of the players (six if there is no dump (an offensive player behind the thrower) and five if thereis one) stand in a straight line down the field (closer to the offensive team's end zone) from the thrower. That line is often vertical (North to South, or more closely parallel to the LENGTH of the field, and not the Width), although some angling can occur. The line is usually straight and may start 5-20 yards from the thrower. Each player in the line is around 5 yards from the next player. In the example above, the first three red players are more or less just a bit removed from that straight line stack. What are the benefits of the Stack? If all of the offensive players are in one part of the field, and if the defense is playing person on(one defensive player guarding one offensive player within 5 yards - and following that offensive player around the field), the stack keeps most of the players in only a small part of the field. This leaves the rest of the field for individual players to move (or "Cut") to. Because all of the offense knows the basic formation that they're playing in, the spaces in the field that are "open" are easier to predict. As the defensive players are usually within a few yards of the individuals that they are defending, individual offensive players can move into the open spaces on the field, and can know exactly what the circumstances will be for them to best be able to take advantage of their individual defender's weaknesses. A well disciplined offense with a tight (team stays close together) stack can provide large portions of the fields for the offensive individuals to work in. In the example above, if we assume that the top left hand red player still had the disc, the first person in the stack would have very clear options for their attempt to get open. They could either cut up the field (North in this picture), or they could cut down (South). Because the rest of the players on their team (and therefor the defenders as well) should still be in the stack, they will have a one on one opportunity with their defender. It is difficult for that first defender to guard both the up field, and the down field cut. What happens when a new offensive player catches the disc? The stack should shift in relative position to the player that is now the thrower. In the example above, for example, the second red player from the top has just received the disc. The other red players should move down the field and to the right. What is the strong side and what is the weak side? The strong side is the side that the Marker (the person defending the thrower) is allowing the thrower to throw to unobstructed. In the above case, the marker had been marking to the left of the screen (i.e. allowing the throw to go to the left). He had been trying to keep the red team from throwing to the right. The strong side was the space on the left side of the stack. In this case, the first person in the stack ran to the weak side. As the defenders usually guard the Strong side more carefully (it is easier to throw to that side per the mark), they weren't able to stop the "break mark" throw. How does a stack break down? The offensive players can lose their relative position to each other. They can all be moving in directions that result in collisions (picks). They can be too spread out (thereby allowing less "open" space on the field). They can take up space too far to the strong side. What are the weakness of even a well run stack? Running an offense from a stack is very predictable. The defense knows which lanes the offense is going to try to take advantage of. Because some of the offensive players may not leave the stack, their respective defenders may range further afield from them. As a result, those defenders can move to open spaces and either get the "Poach" defense, or take up a lot of open space.