With a sharp knife, score top of ham in a crisscross pattern, cutting about 1/4 inch deep.
Rub surface with mustard; sprinkle with cloves.
Bank about 20 medium-glowing coals on each side of fire grill and place a metal drip pan in center.
Place grill 4 to 6 inches above drip pan; grease grill lightly.
Insert meat thermometer into center of thickest portion of ham but not touching bone.
Place ham on grill directly over drip pan.
Cover barbecue and adjust dampers according to manufacturer's directions.
Cook for about 21/2 hours, adding 5 or 6 briquets on each side of fire every 1/2 hour to maintain a constant temperature.
After 2 1/2 hours, add hickory chips (presoak chips in water for 30 minutes) to the fire, if you wish, and begin basting every 15 minutes with sherry.
Cook until meat thermometer registers 135° (about 3 to 3 1/2 hours total).