A radar gun is a device which measures the speed of an object traveling through its field of vision. Radar guns were originally designed for police officers to capture the speed of moving vehicles, in order to identify speeders. It was soon realized that the machines could have other uses, such as helping scouts to determine the speed of pitches thrown. Since the guns are small and easily portable, they have become part of the standard equipment of baseball scouts, who can be seen seated behind home plate at major league, minor league, college and even high school games pointing their devices at the pitcher to get a reading.
Until the 1960s, when the first radar guns were used in baseball, measuring the speed of pitches was an inexact science, or required a pitcher to throw a ball through a specially-rigged set-up where it would trigger successive sensors, thus providing a speed reading. The readings were more accurate than the estimates of the past, but they could obviously not be made in game conditions, reducing their usefulness. Now, most major league and minor league ballparks have their own radar guns set up in permanence, whose readings are shown on the scoreboard for all to see. Skepticism is often expressed about the accuracy of these readings, however, which is why the sight of a scout toting his own portable radar gun is still a common one around ballparks.
The most common type of radar gun is the JUGS gun.