Abstract: An adjustable moment of inertia ball bat has a hollow outer ball bat shell defining an interior cavity having an open distal end. A central shaft is disposed in the interior cavity and a weight is disposed on the central shaft. The central shaft passes through and operatively engages the weight. An interior support secures an inner end of the central shaft and a bat end cap is adapted to be fitted into the open distal end of the ball bat shell. The weight moves in the ball bat shell on the central shaft to operatively adjust a moment of inertia of the ball bat.