Add chicken drumsticks to a large resealable plastic bag (skin on or off as desired). Combine ½ cup maple syrup, ½ cup chili sauce, ¼ cup apple cider vinegar, 1 tsp minced garlic and salt and pepper as desired. Pour over drumsticks in bag.
Seal bag and turn to coat drumsticks. Place in the refrigerator to marinate for 2-8 hours (I marinated mine just a couple hours).
Preheat grill to about 400 degrees F (I had 2 sides on, and one side off so I could move them to indirect heat if need be). Either grease the grill with oil or non-stick, or spray a piece of tin foil with non-stick spray and place on the grill over the heat (*see post for additional explanation). Place drumsticks on the grill, and cook, turning every so often, for 20-25 minutes or until meat starts to fall away from the bone. Keep an eye on them so they don't burn! Move to indirect heat if need be.
While drumsticks are cooking (or you can do this ahead of time if you need to), combine ¼ cup maple syrup, ¼ cup chili sauce, ⅛ cup apple cider vinegar and ½ tsp minced garlic in a small pot. Bring to a low simmer over medium heat and cook, stirring often, until reduced and thickened (about 10-15 minutes). Turn off heat and keep warm until chicken is done.
Brush drumsticks with thickened glaze before serving.