1. Cook pasta according to package directions in salted water; reserve 1/2 cup pasta water. Add broccoli rabe during last 2 minutes of cooking; drain pasta and broccoli rabe and return to pot.
2. While pasta cooks, heat oil in a large, heavy pot over medium heat. Pinch sausage from casing in 1-inch pieces and roll into balls with clean hands, placing meatballs directly in pot. Cook meatballs until browned and cooked through (8-10 minutes). Stir in garlic; cook until fragrant and toasted (2 minutes). Add pasta and broccoli rabe mixture, 1/4 teaspoon each salt and freshly ground pepper, and reserved pasta water; cook, tossing, until pasta is coated with a thin sauce (2 minutes). Divide among 6 bowls.