Place chicken into resealable plastic storage bag. Combine 1/2 cup brown sugar, mustard, vinegar, hot sauce, oil and Worcestershire in 4-cup measure; mix well. Pour 1 cup mixture over chicken. Seal bag; marinate in refrigerator 1 hour or overnight.
Pour remaining mustard mixture into small saucepan. Stir in remaining 1/4 cup sugar. Bring to a boil. Reduce heat; simmer 5 minutes or until sugar is dissolved and mixture thickens slightly, stirring often. Reserve for serving sauce.
Grill chicken on greased rack over medium-high heat 10 to 15 minutes or until chicken is no longer pink in center, turning once. Discard marinade. Serve chicken with reserved sauce.