Heat oven to 400° F.
Pat the chicken dry with paper towels. Rub the chicken, inside and out, with 2 teaspoons of the oil and season with 1 teaspoon salt and 1/4 teaspoon pepper. Place in a roasting pan and cook for 30 minutes.
Meanwhile, in a large bowl, combine the radicchio, vinegar, rosemary, 1/2 teaspoon salt, 1/4 teaspoon pepper, and the remaining oil. Add to the pan and continue cooking until the chicken is cooked through (internal temperature 180° F) and the radicchio is soft and brown at the edges, about 25 minutes. Transfer the chicken to a cutting board and let rest at least 10 minutes before carving.
Divide the radicchio among individual plates and serve with the chicken.