Erm, the green line isnt meant to be parallel to the orange lines. Nor are the orange lines meant to be parallel to each other, as perspective warps how they are presented in the field of view. I will go through it once more. The green line shows the full backs relationship to each other. I plotted the orange lines using the grass cut of the pitch to give some sort of reference for the green line. Its not overly difficult to comprehend. Oh, and the green line doesnt go against the effect of perspective. Check the distance between the green and orange at the top and bottom and theyre the same, ie both full backs were level.