A tennis ball does not diffract through a narrow slit. This is common sense. Quantum and modern physics may have some odd ideas but a tennis ball still behaves like a tennis ball!
It behaves like a typical Newtonian "particle" with mass, momentum, kinetic energy and all the other things you have done in mechanics.
It cannot travel at the speed of light.
It doesn't behave like a wave. Why.
To display wave properties you need to perform an experiment that can show diffraction or interference. This is impossible for the tennis ball given its suggested "wavelength" and other characteristics. How could you do this?
Hence, the ball doesn't display wave properties.