From BR Bullpen
The Face mask or catcher's mask is a piece of equipment worn by catchers and umpires to protect their face from errant throws and foul balls. It consists of wires that prevent balls from hitting the face but allow the catcher full vision, and a circle of padding that absorbs shocks. The mask is worn over a helmet that protects the top of the head. Masks worn by umpires are similar in design.
While the mask afford good protection, it restricts vision and movement, which is why catchers (and umpires) are taught to discard it as soon as the ball is hit. Umpires will keep it in their hand, but catchers, who need their two hands, will throw it away to a spot where it will not interfere with the play. There have been cases of catchers failing to throw their mask sufficiently far and tripping on them, most famously Hank Gowdy who dropped a crucial foul pop-up, as a result in the 1924 World Series.
The mask is the first piece of plate equipment to have been developed: the first models date back to the 1870s, developed from a fencing mask, and replacing mouth protectors, adopted from bare-knuckles boxing, that were used prior to this. Fred Thayer developed the first mask for Jim Tyng, catcher of the Harvard University team, around 1877. Derided at first, the contraption caught on quickly and was in general use by the 1880s. It was then improved by adding padding, replacing the mesh used to cover the face by a few carbon-fiber tubes that allow for better vision. It is now being gradually supplanted by the actcher's helmet, inspired by those worn by hockey goaltenders, introduced by Charlie O'Brien in the 1990s.
 Further Reading
- Chuck Rosciam: "The Evolution of Catcher's Equipment", in The Baseball Research Journal, SABR, Volume 39, Number 1 (Summer 2010), pp. 104-112.