Butterflying chicken allows the maximum amount of surface area to be exposed to the grill. Use the indirect-heat method, as shown in Advice for Grilling Chicken. The coals are medium hot when you can hold your hand above them for just 3 seconds.
Removing Backbone
Set the bird on the cutting board breast-side down. With kitchen scissors or poultry shears, cut closely along one side of the backbone, then the other; discard backbone.
Flattening Bird
Turn the chicken skin-side up with the breast facing you, wings up, legs down. Open the bird as flat as possible. Cover its surface with a large sheet of plastic wrap. Flatten by striking the breast firmly in the center with the smooth side of a meat mallet to break the breastbone.
Tucking Legs into Slits
Halfway between the legs and breastbone, near the bottom tip of the breast, cut a 1-inch slit through the loose skin on either side of and parallel with the breastbone. Insert the tips of the drumsticks into the slits to secure them so they won’t pop up during grilling.