Defense
The goal of the defense is to stop anyone on the opposing team from scoring at all costs. The defense has to watch for fouls though because then they will be outnumbered and that will increase the chance of the offense scoring. Here is a video of my brother teaching the basics of defense.
When a middie beats a middie from the other team, the defenders have to slide. This is very important because if the defender slides to late, the middie can get a shot off. If the middie passes when a defender slides, another defender has to get on him right away and push him away. When the defense gets a clear, (When the goalie gets the ball), the defenders have to get open and when they get the ball, they have to pass it up.
A Defense Video