Pour off all but 1 Tbsp fat from pot and reduce heat to medium-high. Add onion and cook until translucer, about 5min. Add garlic and cook, stirring, until fragrant, about 1 min. Add tomatoes and season with salt and pepper. Cook until beginning to break down, about 3 min. Stir in vinegar and return chicken, skin side up to pot. Bring liquid to a boil. Transfer pot, uncovered, to oven and bake until chicken is cook thhrough, about 30 min.