This effect was proposed and described by Christian Doppler in 1842. As often happens, the first one on the scene got to name the effect, so the phenomenon is now known as the “Doppler Effect.” Many people are familiar with the basic concept, even if they don't quite understand how it works. The short version of the story is that when an object approaches an observer, the wavelengths are compressed, causing the frequency to increase, and as the object moves away, the wavelengths spread out, causing a corresponding decrease in frequency.

In a Sports Radar application it is best that the object be  projected directly in line with the radar gun.

This interesting effect is not just intriguing to observe. Knowledge about the Doppler Effect can allow people to use it for the purpose of taking measurement, particularly in Sports Radar Guns and Traffic Radar Guns. Being aware of the shift in frequency caused by the Doppler Effect, for example, can allow astronomers to determine how far away stars are, and whether they are growing closer or further away relative to Earth.