The tennis ball will not appear in every location of it’s trajectory nor will it skip some on it’s way. It will look to us that time on the tennis ball has slowed down.

Time and space are relative. What this means to your question is simply the speed of the tennis ball must be measured in relationship to something else, namely us on Earth.

If the tennis ball is launched from Earth and goes 99% the speed of light from Earth, then microbes and insects on the tennis ball would appear to be moving very slowly. But on the tennis ball, life would go on normally and life on Earth would appear to be going very quickly.

However, on the tennis ball itself, once that speed is achieved, it will appear that the tennis ball is standing still and Earth is moving away very quickly. If you were little and stood on the tennis ball and turned on a beam of light, the light would leave your flashlight at the speed of light in all directions.

How is that possible since light only travels the same speed in a vacuum? Because time slowed down for you, and so light always travels the speed of light, even though you seem to be normal. That’s why space and time are interwoven in the same fabric, what we call spacetime.

The same for us on Earth. We are orbiting the sun, the sun is orbiting the Milky Way center, the whole galaxy is about to collide with Andromeda, etc. etc. But as far as we’re concerned, we’re standing still and light leaves our beams of light at the speed of light.