At least one device is mounted on or over the bladder wall of an inflatable ball such that a center of mass of the device is located away from a center of the inflatable interior of the ball. The device includes an electronic device. The center of mass of the device defines a first point on the bladder wall coincident with or closest to the center of mass of the device and a second point on the bladder wall opposite the first point. The ball comprises a distributed balancing mass for at least partially rotationally balancing the mass of the device. The distributed balancing mass comprises one or more balancing mass elements on or over the bladder wall. The balancing mass elements are arranged at a plurality of locations spaced around the second point on the bladder wall and closer to the second point than the first point.