painted line

i want to make a man marking the lines on a pitch.i have a good idea how to do the walk cycle and the man pushing the line marking trolley but how would i go about making the white line appear begind him on the green plane as he walks along?thanks

Roubal was working on a method using lattice deformation to bring an extruded, coloured plane from below the surface to above the surface as the lattice moved along it. If you search for Roubal and Lattice in here you should find an example.

He had trouble because he wanted to go around corners and the deformation messed up but for a straight line you should be fine.

I do not quite get the effect which you want to make, but this might do it
also: Make a spline, bevel it,convert to mesh, flatten it and then set it to be animated with build.