The ornamental design for ball toy, as shown and described.
FIG. 1 is a top, front, right side perspective view of a ball toy, showing my design.
FIG. 2 is a front elevation view thereof.
FIG. 3 is a rear elevation view thereof.
FIG. 4 is a left side elevation view thereof.
FIG. 5 is a right side elevation view thereof.
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in the drawings depict portions of the ball toy that form no part of the claimed design. The dot-dash broken lines shown in FIGS. 1, 2, 6 and 7 are for the purpose of illustrating boundaries that form no part of the claimed design.