Rotoscope a dance or sport secene. You need to make single images out of a video sequence, like with an Animated Gif. After this you draw just the outlines of the people involved in the action. The simplest tool is an image editor like Gimp and the path tool (any kind of pen and tablet would be better). Add a layer and alter the transparency the way you can see the underneath image. Use at least 6 frames per second.