An article of footwear is disclosed that includes upper (20) and a sole structure (30). The upper defines an interior void that is configured to receive the sole structure and a foot. A lower surface of the upper defines a plurality of apertures (24a-24f), and the sole structure includes a plurality of projections (32a-32f) that extend through the apertures to form a ground-engaging surface. The projections are connected to a foot-supporting member (31) that remains within the upper. A locking system (25, 37, 35a-35f) is incorporated into the upper and sole structure to secure the sole structure to the upper.