On my 02 Ford Maverick the brake pedal judders sometimes when I press the brakes. Why is this happening.

Most commonly that is due to warped brake rotors. A typical machining will take care of that. In some cases a sticking brake caliper can cause that too. We used to rebuild calipers as part of a standard brake job but today factory rebuilt calipers are so inexpensive that we just purchase them from an auto parts store. Your mechanic will inspect the rotors and calipers to see what will solve this problem.