What Causes Bruising And Tenderness On The Calf?

I have a tender area on the right side of my right calf. It appeared about one month ago, it is reddish in color and color has not changed (except to lighten or seem to go away for a time). It is tender to the touch, not painful. About the size of my hand in area and does not appear to have changed in size. First week or so it was visually apparent and tender. For about two or three weeks it seemed to go away. Now has appeared with same size, color, and tenderness as first appeared.