The frog in the picture is a female. Females are larger and become sexually active much sooner than males. ACFs generally have an excellent immune system which protects them from bacterial, fungal and viral infections and the red sore may go away on is own. Red sores and patches on the skin especially around the leg and groin area could be a sign of "red leg disease" caused by the bacteria Aeromonas hydrophila. This is a dangerous disease that requires immediate treatment. The pictures do not indicate that it is serious. Isolate the sick frog(s). Try Maracyn or Maracyn Plus, use about half of the normal dose (frogs are very sensitive to chemicals). Monitor about a week, the sores should clear up. If there is a vet or university biology lab near by, you may want to have them look at the frog, it is likely they can determine what the infection is. Let us know how the frog is doing.