The ornamental design for barbecue grill, as shown and described.
FIG. 1 is a front perspective view of a barbecue grill showing my new design;
FIG. 2 is a side elevational view thereof; the opposite side being a mirror image;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a side elevational view thereof with cap raised; the opposite side being a mirror image;
FIG. 5 is an exploded side perspective view thereof, the opposite side being a mirror image;
FIG. 6 is a reduced perspective view showing the grill in tow behind a vehicle, the broken lines form no part of the claimed design; and,
FIG. 7 shows the grill with the support disc removed and mounted on an alternate support, the support shown in broken lines forms no part of the claimed design.