Ouch! Hurts just thinking about it. I find there's a spot just below my knee at the side which REALLY hurts when I get a baseball into it, but after 30 seconds or so I get much more ankle mobility. Has to be a baseball though, foam roller doesn't seem to hit it.
Another thing to try is to use a baseball on the soles of your feet. If I do that for a minute or two I get increased flexibility in my ankles and hips.