A chest protector is a piece of protective equipment worn by catchers and home plate umpires. While designs have changed, and the designs of catchers' and umpires' gear are different, the basic purpose is the same: to protect the wearer's chest from foul balls and errant pitches.
Chest protectors were first used by both catchers and umpires in the 1880s, and their designs quickly diverged. Although the first catchers' chest protectors were worn under their uniforms - possibly to avoid criticism from teammates - catchers soon adopted an outside design that they could take off when batting. The basic design was quickly set. The protector is made of heavy padding sandwiched between outer layers with battens to keep it from shifting. It covers the chest and abdomen but has cutouts around the shoulders to give the catcher freedom of motion with his arms. In 1979, catcher Bruce Robinson developed an improvement to this basic design, the "Robby Flap", a flap of material that covers the front of the throwing shoulder but does not impede throwing and which is now standard on all protectors.
Umpires' gear had a more complicated history. For a long time, National League umpires wore relatively small chest protectors underneath their coats, while American League umpires used bulky "balloon-style" protectors. The difference in protector style was supposed to have led to differences in pitch calling. NL umpires, who could crouch lower behind the catcher, were supposed to call more low strikes, while the AL umpires were forced to stand upright and called more high strikes. AL umpires switched to the inside protector in the late 1970s when all new hires in the league were mandated to use the inside protector.
- Chuck Rosciam: "The Evolution of Catcher's Equipment", in The Baseball Research Journal, SABR, Volume 39, Number 1 (Summer 2010), pp. 104-112.