Even mechanical shutter is rolling, at a speed of 1/180 s (as opposed to electronic shutter which is rolling at a speed of 1/15 s).
When shutter speed is (say) 1/2000 s, the first curtain is released and it will take 1/180 s to reach the other end. 1/2000 s after the first curtain is released, the second curtain is released, and now there is a slit that travels at a constant speed, taking 1/180 s to complete, but as the curtains are pretty close, any part of the image is exposed for 1/2000 s (time from first to second curtain passing a given point on the sensor).
If a ball is moving during exposure, it will be distorted. As shutter is travelling bottom to top, and the lens projects the image upside down, the travel direction of shutter on the image when it is upright is top to bottom. If a ball is travelling downwards, it will be stretched vertically as it travels in the same direction as the shutter. If the ball is travelling upwards, it will be squished as it travels in the opposite direction. If the ball is travelling horizontally, it will be stretched diagonally, as shutter slit moves across the frame (because the ball also travels, but horizontally).
Interestingly, the electronic shutter reads sensor top to bottom, and the direction of distortion will be reversed from the one with mechanical shutter. If camera is panned left to right, vertical structures lean to the right with electronic shutter, and to the left (but 12x less so) with mechanical shutter.
This has always been the case with any focal plane shutter.
Distortion of moving objects is less visible if mechanical shutter is used, since it is 12x faster than electronic shutter, but if the object is moving fast enough across the frame, it will still show to some extent.
The easiest way to show this is to pan the camera horizontally when taking a picture of a vertical object (such as a street light post). If camera is panned fast enough, even at 1/4000 s it will still show the distortion.
