Possible pulled calf muscle
I recently went for a bike ride and while accelerating from a stop, my chain came loose and I nailed the bottom of my calf on the pedal. It hurt, of course, but I continued my ride without anything really out of the ordinary other than the pain. I even went for a run on the rubber track afterwards.
After I got home I noticed this thing was way out of whack. It's like I tore something loose that was holding my calf muscle to my lower leg. All the Googling I've done hasn't really given me the information I need. I can stand on my tip toes fine and walk, go up stairs, run etc without much pain. However, when I do a flat footed calf stretch while standing up, I can only go about 15 degrees forward compared to something like 45 degrees on my other leg. I'll see if I can get some images posted on an image sharing site.