I suspect that the ball is not centered in its bounding box cube. If the axis reference is away from any edge, the ball will not rotate on its centroid. It will rotate on the centroid of the bounding box.
As a solution you can explode the ball and then create a new comp. That will place the ball in the center of the bounding box. Rotation using the Move tool (on any of the 24 rotation pick points) will rotate the ball on its centroid.