You cook chicken over direct heat
The Result: Charred skin and rare meat in the thickest part of the breast.
The Fix: Prevent flare-ups that char the skin by manipulating heat. First, establish two temperature zones: Set one side of a gas grill to medium-high and the other to low, or build a fire on one side of a charcoal grill. (Make sure your grate is clean and oiled to prevent sticking.) Start the chicken, skin-side up, on the low- or no-heat side, and cover the grill. After a few minutes, when the fat starts to render, flip the meat, skin-side down. Point the breasts' thicker ends toward the hot side to help them cook evenly. Cover and grill for about 25 minutes. When the meat is done (165° at the thickest part of the breast), crisp the skin on the hot side for a minute or two, moving it as needed to avoid flare-ups. Wait until the last few minutes to brush on barbecue sauce: The sugars in the sauce will char quickly.