Place chicken, breast side down, on barbecue grate; top with weight. (See tip.) Grill 5 min. Remove weight; turn chicken. Grill (without weight) 35 min. or until chicken is done. Brush chicken with 1/2 cup barbecue sauce; grill 5 min. Remove from barbecue; brush with 1/4 cup of the remaining barbecue sauce. Cover to keep warm.