Abstract: Methods of and apparatus for detecting pitches which are illegal in the game of slow pitch softball by virtue of their having exceeded a maximum allowable height of twelve feet in traveling from the pitcher's mound to home plate. Infrared, visible, or ultraviolet light is reflected from a ball reaching a height above the permitted maximum to a detector which is incorporated in a unit typically mounted on the backstop at the appropriate height. The light which is reflected may be natural light, or the light may be generated in and propagated from the backstop-mounted unit. In both cases, the impingement of the reflected light on the detector causes that component to output an electrical signal which is amplified and employed to drive a sound generator, thereby providing an audible warning that an illegal pitch has been thrown.