Mix ketchup, brown sugar, vinegar, Worcestershire sauce, cumin, paprika, grated garlic, 1/2 teaspoon salt, and a few turns of pepper in a large resealable plastic bag.
Add the chicken to the bag, seal it tightly, and massage gently to coat the chicken with the marinade.
Refrigerate the chicken for 2 hours, or freeze it for up to 1 month. If frozen, defrost in the refrigerator overnight before cooking.
Remove the chicken from the bag and grill it over indirect heat, covered, for 20-25 minutes, until cooked through, lightly charred, and the internal temperature reaches 165°F.
