Tactical Use
Inside pitching is a common and legal tactic in baseball, and many players make use of brushback pitches, or pitches aimed underneath the chin, commonly referred to as 'chin music', to keep players away from the plate. "Headhunter" is a common term for pitchers who have a reputation for throwing these kinds of pitches. However, throwing at a batter intentionally is illegal, and can be very dangerous. When an umpire suspects that a pitcher has thrown at a batter intentionally, but is not certain, a warning is issued to the pitcher and the managers of both teams. From that point on, any pitch thrown at a batter can cause the pitcher and the manager (if believed to have ordered the pitch) of the offending team to be ejected immediately from the game. Serious offenses such as a ball thrown at the head (called a beanball) can result in the immediate ejection of the pitcher, and the manager if he ordered the beanball, even without a warning. If the umpire is certain that the pitcher intentionally hit the batter with the pitch, the pitcher is ejected from the game with no warning.
Often, if a player is acting rude or unsportsmanlike, or having an extraordinarily good day, the pitcher may intentionally hit the batter, disguising it as a pitch that accidentally slipped his control. Managers may also order a pitcher to throw such a pitch (sometimes called a "plunking"). These pitches are often aimed at the lower back and slower than normal, designed to send a message more than anything else. The opposing team usually hits a batter in retaliation for this act. The plunkings generally end there because of umpire warnings, but in some cases things can get out of hand, and sometimes they lead to the batter charging the mound, bench-clearing brawls, and several ejections. Such plunking duels are more common in the American League than in the National League, because in the NL the pitchers must bat for themselves and open themselves up to direct retaliation (although hitting a fellow pitcher is a serious breach of baseball etiquette).
Read more about this topic: Hit By Pitch