The ornamental design for a support for a grill, as shown described and illustrated herein.
FIG. 1 is a top plan view of a support for a grill, showing our new design;
FIG. 2 is a bottom plan view thereof; and,
FIG. 3 is a side elevational view of one side thereof, the other side, front and rear elevational views being the same.
In FIGS. 1 and 2, the dashed lines in the figures represent environmental subject matter and form no part of the claimed design, and the dotted lines represent the borders between claimed subject matter and unclaimed environmental subject matter, and form no part of the claimed design.