How to Make It
In a medium saucepan, combine all of the ingredients and bring to a boil. Simmer over moderate heat, stirring occasionally, until reduced to 1 1/4 cups, about 7 minutes. Strain the sauce through a fine sieve and let cool completely; discard the solids.
Spread the duck skin on a work surface and, using a sharp knife, scrape off any excess fat. In a large skillet, cook the skin over moderately low heat, flattening it with a spatula, until golden and nearly crisp, 15 to 17 minutes. Transfer the skin to a rack to drain and crisp, then break into small pieces.
Meanwhile, in a food processor, combine the breast and leg meat and pulse until finely chopped. Scrape the chopped meat into a large bowl and add all the remaining ingredients except the oil and mix well. Form the mixture into 1-inch balls and thread onto bamboo skewers.
Light a grill or preheat a grill pan; oil the grate. Brush the meatballs with oil and grill over moderately high heat, turning, until lightly charred outside and medium within, about 6 minutes. Transfer the skewers to a platter, garnish with the crispy skin and serve with the sauce.