Abstract: An athletic base system is provided having a ground support structure that releaseably secures an athletic base thereto, the ground support structure having an upper base-mounting surface, and a member for securing the structure in position relative to the ground, the base mounting surface having a fastening element in the form of a nipple having at least one relief zone within the volume occupied by the nipple to facilitate inward deflection of radially extending parts of the nipple when the nipple is joined with a nipple receiving recess on the bottom of the base as the base is being mounted on the ground support structure.