An article of footwear is disclosed that includes upper and a sole structure. 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, and the sole structure includes a plurality of projections that extend through the apertures to form a ground-engaging surface. The projections are connected to a foot-supporting member that remains within the upper. A locking system is incorporated into the upper and sole structure to secure the sole structure to the upper.