The ornamental design for a composite ballbat, as shown and described.
FIG. 1 is a perspective view of a composite ball bat embodying the principles of the present invention
FIG. 2 is a top view of the composite ball bat; the bat is symmetrical about its longitudinal axis, and this view accordingly remains the same as it is rotated through an arc of up to 360 degrees;
FIG. 3 is a left-hand end view of the composite ball bat; and,
FIG. 4 is a right-hand end view of the composite ball bat.