After evaluating the poster more, I thought that adding a pen, and maybe some use of scribbling to suit the whole drawing your design’s theme of the poster. To do this, I vectorized a picture of a pen, adjusting the threshold so that the pen was fully black and added it to the poster. To add scribble, I used the pen tool, underneath the pen as if it had just drawn it, and also an abstract scribble on the shoe itself.
This is the final result. . .Competition advert