Point blocking is a defensive technique in Ultimate Frisbee. Basically, it is blocking the throw of the person you are marking with your hand or foot. Since you are probably standing within about 2 feet of the person you are marking, point-blocking someone requires you to have quick hands or feet and an ability to predict where they are going to throw. You basically have to let the person think that they are going to be able to throw somewhere, but already know that they are going to be throwing there, and then just as they release the throw, stick your hand or foot there. It's hard, and there is no good way to learn to point-block. If you have a good mark, quick hands, and can watch the eyes of the person you are marking to see where they are about to throw it, you might be able to get a point-block. Try and keep your hands low, and your elbows in so that you can stick your hands out more quickly. The people who get point-blocks also tend to be willing to take a step off the mark, so as to get an extra half second to react to the throw. Generally, you don't want to try and get a point-block though. If you get one, great, but if you can just shut the thrower down so that he doesn't even attempt a throw, that's probably better.