How about cheating? You can pass this onto your teacher if (s)he points out that this isn't a problem of worldly magnitude you can say:
"cheating is an unethical practice and ethics is a worldwide problem so I decided to start somewhere where I clearly understood the dynamics of the situation and obstacle"
Anyway... focus it on wipers. Different techniques and custodies to prevent it - like ball technology and clothing materials. Maybe talk about producing a ball that splats and leaves a mucus like paint so it is very hard to wipe, or a ball that breaks and mists so that wiping would be extremely difficult because the paint goes everywhere instead of being concentrated where it hit. Maybe talk about clothing that holds onto paint because of special fibers or changes color due to a temporary chemical reaction so wiping would do nothing to remove the mark of the hit.
Lots of possibilities.
