1. Preheat grill to medium-high heat.
2. Rub the drumsticks lightly with oil to avoid sticking to the grates.
3. Place the drumsticks on the grill and cover. Let cook for about 20 minutes, turning once or twice during cook time.
4. If there are flare-ups, try to move the chicken to a different part of the grill.
5. Meanwhile, combine the ketchup, soy sauce, rice vinegar, and red pepper flakes in a bowl and mix well.
6. Brush cooked chicken liberally with sauce immediately after removing chicken from grill.
7. Sprinkle with scallions and let sit for five minutes before serving.