The ornamental design for a supportstand for athletictraining device, as shown and described.
FIG. 1 is a front right side perspective view of the support stand of the
present invention showing my new design, the broken line depiction of the
ball and tether being for illustrative purposes only and forming no part
of my new design;
FIG. 2 is a front elevational view thereof; and,
FIG. 3 is a right side elevational view thereof.
The surfaces or portions of the article not shown in the drawing or
described in the specification form no part of the claimed design.