The ornamental design for the case for an overhandthrowingtrainer, as shown and described.
FIG. 1 is a front perspective view of the overhand throwing trainer showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken line showing of optional engraved labeling, surface indicia, support structures, and anchoring structures are included for the purpose of illustration only and forms no part of the claimed design.