The ornamental design for a holster for a hammer, as shown and described.
FIG. 1 is a perspective view of a holster for a hammer showing our new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a rear elevation view thereof showing a dashed out belt;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines in FIGS. 3, 4, 5, 6 and 8 showing a clasp illustrate portions of a holster for a hammer that form no part of the claimed invention. The broken lines in FIGS. 1 and 2 showing a logo outline illustrate portions of a holster for a hammer that form no part of the claimed invention. The broken lines in FIG. 4 outlining a belt show environmental matter and illustrate matter that forms no part of the claimed design.