Here above is a photo showing two such balls right in front of a zebra crossing. This is where, while watching for traffic, I have personally tripped over the ball and fell
straight on my face. My shoulder still hurts from the fall. It even makes a mockery of the ramp intended for wheel chairs.
And here below is another example of misplaced balls. When you sit in the car ready to move off, you do not expect a ball to be in your way. Sitting in the car you cannot normally see it. From the scrape marks on the balls you can see how many cars have gone over them causing damage to the vehicle.