In a large bowl, mix together chuck, pork, bread crumbs, eggs, Parmesan, Pecorino, garlic, parsley, and red pepper flakes until thoroughly combined. Roll out meat mixture into balls 1 1/2 inches in diameter. Season meatballs all over liberally with salt and pepper.
Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over entire surface of coal grate. Set cooking grate in place, cover gill and allow to preheat for 5 minutes. Clean and oil the grilling grate. Brush meatballs with olive oil and place on grill and cook until well browned all over and cooked through, about 8 minutes total, 2 minutes per side.
Remove meatballs to a platter and let rest for 5 minutes. Serve with marinara sauce.