It's been a while I practiced a human leg.
Achieving a realistic result of a foot can be challenging especially when it is in an unusual position. This particular piece is not exempted as I rallied to get a good feel of a foot from the top view.
If one us not careful, he could ultimately end up sketching something else especially since it has to do with pen.
If you want to get such result, you will have to understand the shape by getting an accurate outline - as you can see in my first step - and rhythmical flow of your strokes according to the contours of the leg you are working on. Study the veins around it.
This piece was done with a blue ballpoint pen on a cardboard paper using scribble style. You can see my steps below:
Thank you.