That all depends on if you want pizza with little meatballs that are raw on the bottom, which, of course, we assume you do not. Meats such as ground beef, sausage, and bacon do need to be cooked before going on the pizza.

In the first place, you really want them cooked through, and nestled in a bed of cheese and tomato sauce, they are unlikely to get done before the rest of the pizza is overcooked - especially if you are using large chunks or forming them into meatballs. Second, they throw off a lot of fat as they cook, and you really don't want it oozing all over the surface of your pizza. You don't need to cook them to death, though, because they will be heated again on the pizza.

Pepperoni, prosciutto, other cured meats, and cooked deli meats do not need to be cooked before going on a pizza.