The Pitching Rotation and the Bullpen
Major League Baseball teams will normally carry eleven or twelve pitchers on their roster (eleven pitchers, and thirteen "position players" are considered the minimum, with the twenty fifth position normally being down to managerial preference).
The pitchers can normally be divided into three distinct roles:- the starting rotation, the middle-relief and the late-innings relievers. The middle-relief and late-innings relievers form what is known as the "bullpen".
As with the hitters, pitchers can be substituted at any time by another pitcher. Again, if pitcher is replaced, he cannot then return to the game.
The Starting Rotation
In modern day baseball, teams generally have five starting pitchers, and they take it in turn to start a game every fifth day (hence the phrase "rotation"). Sometimes, if the schedule pans out, a team can get away with a four man rotation, and in the distant past some teams managed a three man rotation. However, in modern Baseball it is generally accepted that a starting pitcher needs four days of rest before he can take his next turn to start.
The starting pitcher will generally throw between 90 and 120 pitches before he is removed from a game by his manager (unless he gets battered early on and "chased from the game"). The expectation is that this will get him through anything from 5 to 8 innings, and the further he goes the better.
Each team will have an "Ace", who is the no.1 pitcher in the rotation. He is expected to win most of his games, and also pitch "deep" into most of his games, not requiring much support from the bullpen. A good team will have a no.2 pitcher almost as good as the ace, but the further down the rotation you go the lesser the pitcher. The no.5 pitcher is often an up-and-coming youngster, who if the schedule allows will miss his spot in the rotation. Ideally, the no.5 pitcher never gets used - you hope he'll win his start, you don't expect it.
Managers will often try and match up rotations. Sometimes it's a case of being aggressive, and matching up your no.1 with their no.1, your no.2 with their no.2 and so forth. However, equally a team can benefit from getting rotations out of kilter, throw your no.5 at their no.1 (expecting him to get beaten), then your no.1 at their no.2, your no.2 at their no.3 and so forth. Effectively by conceding one major mismatch you may get the advantage in the other two (or more) games of a series. Each game only counts as one win!
The modern day focus on "pitch counts" places even more of a premium on "patient hitting". If a hitter can face 10 pitches before finally getting out, he's done a good job of getting the pitcher towards his pitch count (usually a team will allow a pitcher so many pitches, and will remove him, even if he says he feels OK), so even though the hitter hasn't got on base, he's helped the team by shortening the starting pitcher's time on the mound.
Starting pitchers are generally most vulnerable in the first inning (whilst they're getting into the rhythm of the game) and then towards the end of their stint. One of the key decisions of a manager is when to remove a starting pitcher and bring in a replacement - you don't want to do it whilst he's still throwing well, but you don't want to leave him in too long either. Judging when he's "starting to toast" but not waiting for him to "burn completely" is critical.
The Late Innings Relievers
Most teams have a specialist "closer", who generally only pitches in the ninth inning, when the team has a short lead. This is the most pressurised pitching position, as the game is on the line and the opposition will use any pinch hitter available and take any risk to try and score a run.
Many teams also have a "setup pitcher" (or two) who will pitch the eighth inning (or if the closer is unavailable, does the closer's job that night). The position is similar in many aspects to the closer, but the pressure isn't quite as great. He's only pitching in the "last-but-one chance saloon"!
The closer and setup pitchers generally won't pitch more than one inning per game, so it's quite common that a closer or setup pitcher can pitch in two or three consecutive games before they have to take a day off to rest. However, managers will generally only use them in close games - you want to have them available in a tight game and not fatigued from the day before.
The Middle Relief
In an ideal game the starting pitcher goes seven innings, hands over to the setup man who pitches the eighth, the closer closes out the ninth, and a team goes home victorious. Actually, in an ideal world the starter pitches so well that he's able to pitch into the eighth or even the ninth (a "complete game") and the team's bullpen don't have to pitch at all and get a day's rest.
Ideal games aren't very common.
More often than not, the starter won't get as far as the end of the seventh inning, and will come out some time in the sixth, or the seventh. Or he'll simply not be pitching well that night and get pulled from the game very early to give the team some chance of staying in touch in the game. In all of these circumstances, the teams remaining four or five pitchers have to come in and hold the fort. These are the "middle relief".
The normal job of the middle relief is to get from the starting pitching to the setup man and closer, but teams will usually have a "long reliever" within the bullpen. This is by far the most soul destroying position on the team, as this pitcher will usually only come in when a starter has been chased from a game early, so effectively his manager has given up on winning the game already (but someone has to come in and pitch six or seven innings to get them to the end - you don't want to use up the rest of the bullpen on a lost cause).
The rest of the middle relief have a high pressured job, and very little glory to be gained. Normally they'll come in because the starter has just shown that he's starting to get tired (often by putting his last couple of hitters on base), so the middle reliever often comes in with runners already on base (and in the past, were consequently referred to as "firemen").
A team's weakest pitchers tend to play in middle relief, because the hope is they won't play at all. Quite often the highest scoring innings come in the phase when the starter has gone, but the late-innings relievers haven't been reached yet.
The middle and late-innings relievers don't sit on the bench with the rest of their team, but normally sit in a warm-up area known as the "bullpen". It generally takes a pitcher five to ten minutes to get warm, so when the manager thinks he may need a pitcher out of the bullpen, you'll see a telephone call made to the bullpen to get a pitcher warming up.
Quite often a pitcher will warm up in the bullpen because the pitcher on the mound is getting into trouble and may need replacing. Then the pitcher gets himself out of the jam and the bullpen pitcher sits down again. There's only so many times a pitcher can warm up without risking injury though, and it may be that after a couple of false alarms he's no longer available to pitch in that game.
Which pitchers a manager will use from the bullpen is a decision made on the spot. Sometimes he may be restricted by fatigue (if a bullpen pitcher pitched two or three innings the day before, he may not be available for that game), sometimes it may be dependent on the hitter coming up (a left handed pitcher is brought in to face a key left handed hitter), sometimes it may depend on how many innings it's hoped he'll be able to cover.
Replacing a Pitcher
A pitcher can be replaced at any time, though it's generally considered poor etiquette to do it in the middle of an at-bat (unless the pitcher is injured). To replace a pitcher the manager (or sometimes the pitching coach) will walk out as if to talk to him (he is also allowed, once per inning, to simply visit the pitcher and talk to him - perhaps to calm him down or simply see if he's getting tired), and then ask him to hand him the ball. The pitcher then walks off (perhaps to applause from the fans, perhaps not!) and the new pitcher comes in from the bullpen.
The new pitcher should be ready to pitch straight away (hence you'll sometimes see the pitching coach come to the mound beforehand, simply to buy some time for the replacement to get warm) but if the pitcher on the mound is being replaced because of injury, the new pitcher is allowed to warm up on the mound.
There are no ties in baseball, so if the score is level extra innings are played. Sooner or later the bullpen may be exhausted and there's no-one left. Most teams will normally have one or two position players (i.e. hitters) who have some experience of pitching, perhaps in high school, perhaps in warmups, and eventually they may get a turn on the mound. Look at a box score of a game that went to 14, 15, 16 innings and you'll see some very unlikely pitchers at the end!
Pinch Hitters and Double Switches
One key difference in the Major Leagues is the use of the designated hitter. In the American League, where the designated hitter (DH) bats instead of the pitcher, life is much simpler. There's no decision to be made in late innings when the pitcher's turn to bat comes due.
However, in the National League, where there is no DH, managers have decisions to make. If a team is tied or losing in a close game, in the late innings, and the pitcher is due up to hit, then the manager may decide he cannot "waste" an at-bat by allowing the pitcher to hit for himself, and he'll bring in a pinch hitter to hit for the pitcher, and then at the start of the next inning replace the pinch hitter with a new pitcher from the bullpen. Often a starting pitcher in the National League won't go as deep into games as an American League counterpart because he is removed for tactical reasons.
An alternative strategy in the National League is to make a "double switch". If the team are changing pitcher anyway and the pitcher's spot is due up to hit in the next inning, they may make two substitutions at the same time. A position player replaces the pitcher (in the batting order) but at the same time a pitcher replaces a position player (presumably one who has recently hit) so the team still has a pitcher on the mound, but he won't have to hit shortly.
Example: at the bottom of the 7th inning, the pitcher is due to "lead off" as the 9th hitter. In the top of the 7th the current pitcher is replaced by a reserve outfielder (who therefore now hits in the 9th spot) and an outfielder (who has just hit 8th in the order) is replaced by a pitcher from the bullpen (who pitches, but now has eight hitters ahead of him before he is due up). This is a double switch.
Managerial strategy without the Designated Hitter is often much more complicated!
Junking a Game
With the regular season being 162 games, there comes a point when a manager may decide that a game is a lost cause, and instead of bringing in his best bullpen pitchers, he'll leave a lesser pitcher out there to finish the job, and keep the better pitchers fresh for the next few games. For a pitcher designated for "long relief" this is his job, and to a lesser extent for the lower pitchers in the rotation. You hope your no.5 starter will win some games, but you don't always hang your hat on it (and if you do, expect to lose it).
Every team always tries to win every game, but any manager will concede there are some he expects to win more than others, even if he won't say so.
Shutouts, Complete Games, No-Hitters and Perfect Games
If a pitcher manages to complete all nine innings then he's said to have pitched a complete game. If he doesn't concede a run it's a complete game shutout.
If a pitcher manages to complete all nine innings without allowing a single base hit then it's known as a "no hitter". Even more rare is a "perfect game", in which no base runners at all (so no hits, no base on balls, no hit batters) are allowed. There have been about twenty perfect games in the history of Major League Baseball, depending on how you count them! On two occasions a pitcher has pitched a perfect nine innings, but the score has remained tied at zero, and he's lost the perfect game in extra innings.