Chop 2 bunches broccoli rabe into 1-inch pieces. Cook in salted boiling water until crisp-tender, about 3 minutes. Drain well. Cook 4 smashed garlic cloves in 1/4 cup olive oil in a large skillet over medium-high heat, stirring, until golden, about 3 minutes. Add a pinch each of red pepper flakes and salt, then add the broccoli rabe; cook, stirring, until heated through, 2 to 3 minutes.
The sauce for these meatballs is slightly chunky. For a smoother sauce, puree with an immersion blender.