It broadly falls into two categories. The first, rarer case is trading beanballs (pitches that hit the batter). Pitchers routinely pitch inside, or close to the batter, to get him to back away from the plate (making it harder to hit pitches that are on the side of the plate opposite the batter). Sometimes, though, the pitcher's command isn't as good as he thinks it is, and he hits the batter when he tries this. If this happens a few times (once or twice can be an accident; more is seen as reckless/intentional), the other team's pitcher might throw near or at a batter on the first pitcher's team. Sometimes, in this case or the second version, the pitcher who throws at someone is the person targeted for retaliation, but this is complicated by the fact that, in one of the two divisions that compose Major League Baseball, pitchers do not have to hit, which means you can't directly target the person who is targeting your teammates.
The second, and more common, is a perceived violation of baseball's unwritten rules. There are a lot of these, but they mostly boil down to "don't have too much fun" and are exceedingly stupid. Things that are seen as violations of these unwritten rules include:
- Hitting a home run and watching it go over the wall
- Taking too long to run around the bases after hitting a home run
- Taking too long to go to first base after drawing a walk
- Flipping your bat after a hit
- Stealing a base while you're up by a lot or down by a lot
- Bunting for a hit (trying to tap the ball with your bat rather than really hit it) to break up a no-hitter (a game where a pitcher has not surrendered any hits, a very rare occurrence)
Basically, pitchers are sensitive babies and they will throw a 95 MPH projectile at you if you hurt their feelings by being better than them. Sometimes breaking these rules will result in an exchange of hit-by-pitch events (you hit my guy, whether arbitrarily "justified" or not, so I hit you/your guy). Bizarrely, this is tolerated, but if the hitter decides he wants retaliation in an equally violent way (say, by walking up to the pitcher and punching him), this is considered completely unacceptable. I love baseball, but it's a really dumb sport in some ways.
The second, and more common, is a perceived violation of baseball's unwritten rules. There are a lot of these, but they mostly boil down to "don't have too much fun" and are exceedingly stupid. Things that are seen as violations of these unwritten rules include:
- Hitting a home run and watching it go over the wall
- Taking too long to run around the bases after hitting a home run
- Taking too long to go to first base after drawing a walk
- Flipping your bat after a hit
- Stealing a base while you're up by a lot or down by a lot
- Bunting for a hit (trying to tap the ball with your bat rather than really hit it) to break up a no-hitter (a game where a pitcher has not surrendered any hits, a very rare occurrence)
Basically, pitchers are sensitive babies and they will throw a 95 MPH projectile at you if you hurt their feelings by being better than them. Sometimes breaking these rules will result in an exchange of hit-by-pitch events (you hit my guy, whether arbitrarily "justified" or not, so I hit you/your guy). Bizarrely, this is tolerated, but if the hitter decides he wants retaliation in an equally violent way (say, by walking up to the pitcher and punching him), this is considered completely unacceptable. I love baseball, but it's a really dumb sport in some ways.