Mix together balsamic vinegar, lemon juice, olive oil, rosemary, red pepper flakes, garlic, salt and pepper.

Place chicken in a glass or ceramic baking pan or ziplock bag and pour marinade over chicken.

Cover and refrigerate at least 4 hours or overnight (preferred).

Preheat grill to medium.

Grill chicken for about 10-15 minutes (depending on the size of the pieces) brushing with reserved marinade and turning once so they brown evenly.

Chicken is done when the meat thermometer registers 165°F or the inside is not pink.