A 62-year-old man with poorly controlled diabetes mellitus presents with 2 days of progressive pain and redness of his right lower leg. He reports fever and chills. Examination shows a warm, tender, erythematous plaque over the anterior shin measuring 12 cm in diameter with indistinct borders; there is mild nonpitting edema. No fluctuance is appreciated. There are no hemorrhagic bullae, skin anesthesia, or crepitus. A faint erythematous streak extends proximally toward the groin. Which of the following best describes the depth of involvement and most likely diagnosis of this infection?