I was at the Boston Regional doing field repair/reset, and we did check the balls as we reset the field after every match, and replaced the broken ones with new ones. If one of the strips of the ball had snapped and was poking out of the fabric, it came off the field. If all the strips were connected and round but the fabric was slightly torn, or it had grease spots on it, it stayed on the field because it was still perfectly functional. We found one ball covered in blood (who knew robots could bleed?
) which came off the field because it wasn't sanitary... I think you'll find that people will use common sense, and the balls will all be in pretty good condition.