From BR Bullpen
A bean ball (aka chin music) is a ball thrown with intent to hit the batter, often in the head. A batter hit by a bean ball is said to have been beaned. A bean ball should not be confused with an ordinary brushback pitch, which is intended to intimidate the batter rather than hit him.
Bean balls, especially those targeting the batter's head, can be extremely dangerous. Ray Chapman, the only major leaguer killed during a game, was fatally beaned. Ottis Johnson was the last minor league player to be fatally beaned during a game. Beanballs have cut short the careers of other players, notably Mickey Cochrane, Tony Conigliaro, Dickie Thon and Kirby Puckett. Because of the grave danger of bean balls, players take beaning attempts- or what they think are beaning attempts- very seriously. This often results in charging the mound and bench clearing brawls. Ironically, it can also lead to beanball wars, in which each team tries to retaliate for previous beanings.
According to the rules of baseball (Rule 8.02d), beanballs are strictly forbidden. The umpire may eject from the game any pitcher he believes is guilty of throwing at the batter, though he normally will not eject a pitcher before warning both teams. The umpire need not wait for an attempted beaning before giving a warning. In cases where there is bad blood between the teams, he may even warn them before the start of the game. In addition to ejecting the pitcher, the umpire is allowed to eject a manager who he believes ordered a bean ball attempt.