In ultimate frisbee, a forced turnover. A D is a very very good thing, and are reasonably rare. Our team is doing pretty well to get 10 Ds in a game, even against a weak team. Lay out Ds are even better, because they are much much cooler and more bad-assed. After a D, you should not pick up the disc, because it is very likely that you will throw the disc away from all the adrenaline pumping through your body. If you do happen to catch on D, i.e. intercept a pass by the other team, you should look dump right away. A D does not have to be an interception. Anything that forces a turnover, a point block, a blocked pass, or knocking the disc out of bounds is a D.