Mix together all spices for spice rub in a small bowl.
Liberally sprinkle spice mixture all over chicken. Use your hands to lightly rub into chicken, getting under skin when possible. Allow to sit for at least an hour, but overnight is better.
On a gas grill
The only way to know that your chicken is fully cooked is to use an instant read thermometer, like this one. Be sure to have one on hand.
Heat all burners on the grill to medium heat. Arrange chicken skin side down on the grates and cook with the lid closed for about 4 minutes. Flip the chicken over, then close the lid and cook for another 4 minutes. Repeat this until the internal temperature of the chicken reaches 165 F. This should take about 15-20 minutes total.
Towards the end of the cooking time (after flipping chicken 3-4 times) brush chicken with BBQ sauce. Brush one side, flip, and brush the other side. Chicken should be done or almost done when you brush with the BBQ sauce so the sauce doesn't burn. The chicken can stay on the grill for a few minutes after brushing with sauce to allow the sauce to thicken and glaze the chicken.
On a charcoal grill
The only way to know that your chicken is fully cooked is to use an instant read thermometer, like this one. Be sure to have one on hand.
Light charcoal using your preferred method (chimney or lighter fluid). When flames have died down and charcoal has ashed over (usually this takes about 20 minutes) arrange the charcoal in an even layer in the bottom of the grill.
Arrange chicken skin side down on the grates and cook with the lid closed for about 4 minutes. Flip the chicken over, then close the lid and cook for another 4 minutes. Repeat this until the internal temperature of the chicken reaches 165 F. This should take about 15-20 minutes total.
Towards the end of the cooking time (after flipping chicken 3-4 times) brush chicken with BBQ sauce. Brush one side, flip, and brush the other side. Chicken should be done or almost done when you brush with the BBQ sauce so the sauce doesn't burn. The chicken can stay on the grill for a few minutes after brushing with sauce to allow the sauce to thicken and glaze the chicken.