It's a piece of protective equipment the catcher (and the home plate umpire) wears to keep from being struck in the face by the ball.
If the pitcher is not on the pitcher's plate, he can turn as far as he wants to look at the runner on first base. If the pitcher is on the pitcher's plate, and his shoulder turns more than 45 degrees toward first base (halfway between home and first), it is generally interpreted to be a pick-off attempt.
This is not a requirement, but is done as a courtesy to the catcher. The umpire can also take this opportunity to talk to the catcher and not make it seem obvious. This practice was started many years ago, to be honest, so that the umpire would not show their rear end to the fans primarily behind home plate. Most conversations between the umpire and the catcher occur while both are facing the pitcher (toward centerfield)..that way no fan can see either player or umpire's face, read lips or even tell that an umpire and catcher are talking.
In baseball, in order for a batter to be called out after the third strike, the catcher must catch the ball without it hitting the ground. If he does not, and there is no runner on first base, or there are two outs, the batter becomes a batter-runner. At this point, in order to make the out, the catcher must either tag the runner, or throw the ball to first for a force-out. Regardless of the outcome of the play, the pitcher is still awarded a strike-out. As an illustration, a pitcher can face two batters, and strike them both out. A third batter comes to the plate, receives three strikes against him, but due to an uncaught third strike, reach first. A fourth batter can then come to the plate, strike-out, and thus award the pitcher with his fourth strike-out in the inning.
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The batter faces towards home plate, with their feet just further than shoulder width apart. If the batter is right handed, they will stand to the left of the plate, looking over their left shoulder at the pitcher. If the batter is left handed, they will stand to the right of the plate, looking of their right shoulder at the pitcher.
Face Plate is used on Lathe machine. It is just like lathe chuck. irregular shape job clamp on face plate by clamps, bolts.
It protects the catcher when a batter foul a pitch off the mask It blocks the ball from hitting the catcher in the face
On July 15, 1998, Astros closer Billy Wagner was hit in the face by a line drive off the bat of catcher Kelly Stinnett of the Arizona Diamondbacks at then-named BankOne Ballpark (now Chase Field) in Phoenix
A removable face plate helps to deter theft if removed upon exiting the car.
The edge should face away from the plate.