The fielders back up the pitcher. Most of the duty to get the batter and runners out falls on their shoulders. Their glove and footwork can make or break a game for a pitcher. It is, in fact, for this reason that there are 'un-earned runs.' If a fielder makes an error and the batter allowed on scores, the run is not charged to the pitcher for stats purposes because he did everything he could to prevent it.
Fielding is more about positioning than positions. Instead of saying that the shortstop plays balls hit between second and third base, say that he plays anything he can handle more easily than the players around him. This is why players will adjust their positions according to the batter, the pitcher, and other factors.
Perhaps the most famous example of this is the 'Ted Williams Shift.' Ted Williams was one of the best hitters in the 1940s and '50s, but opposing team noticed that he got most of his hits to right field. Because of this, they'd shift their players and overload that side of the field to have a better chance of getting him out1. The result was that the third baseman ended up covering second, and the second baseman played shallow right-center field.
The most basic elements of fielding, 'put outs,' are the fly out, force out, and the tag out. There are various forms of each of these, which in turn are combined to make more complex plays.
A fly out occurs any time a fielder catches a batted ball before it hits the ground. Its variations include the line out, in which the batter hits the ball with low arc and high velocity and the pop out, in which the ball arcs very high over the infield.
Most force outs occur when a fielder catches a bounced ball and throws it to first base. The technical definition of a force out means a fielder posesses the ball at a base that an advancing runner is 'forced' to go to by a runner following. For example with a runner on first, if the batter bounces a ball to the second baseman, the second baseman can catch the ball and step on the base to get the runner out.
When the fielder scoops a rolling or skipping ball off the dirt and throws to first, it's called a ground out. A high bounce from just in front of homeplate is a chopper. And if the fielder catches it in the air after one or two bounces it's called a one or two hopper respectively.
Simply enough, when a fielder posesses the ball and tags the runner with his glove, it is a tag out. These don't occur very often because it's so much easier just to throw to the base. When these do occur, it's usually at homeplate as a runner tries to score. Called a play at the plate, it's one of the most exciting in the game.
How 'Bout That
Most of the more advanced fielding are combinations of the more basic plays. These however can turn the feel of a game around. They can dishearten the opposing team and can even spark the offence into getting a few more runs.
- Two outs recorded on any one play are called a double play. 'Turning' the double play most often involves a runner on first forced out at second followed by the batter being forced out at first.
- A special form of double play is called doubling off a runner. In this, a runner who goes on contact in a fly out is off base when the ball is caught. Before he can get back to base and 'tag up' the fielder throws the ball to that base for a force out.
- Yet another double play is the strike 'em out, throw 'em out. Just what it sounds like: the pitcher strikes out the batter and a runner is caught off base (usually stealing) and tagged out.
- Similar to but much rarer than the double play is the triple play. The simplest form is 'going round the horn' forcing runners at third, second and first base.
- Extremely rare is the 'unassisted' triple play. Normally a second baseman or shortstop catches the ball on a line out with runners 'in motion.' He then tags the runner going to second and steps on the base doubling off the runner going to third (because the ball was caught in the air).
- In a pick off the pitcher, instead of throwing to homeplate, throws behind a runner 'leading off' preparing to steal. If he's fast enough, and the runner too slow, the baseman can 'apply the tag' before the runner gets back to base.
- Though somewhat out of fashion in the ettiquite conscious leagues of today, the hidden ball trick still shows itself from time to time. In this bizzare and tricky play, a 'meeting on the mound' is called and the pitcher secretly gives the ball to the first baseman. When the meeting is over and positions retaken, the pitcher sets as usual; the first baseman shows the ball to the umpire, waits for the runner to take his lead, then tags him with the ball. It's very obscure, but shortstop Ozzie Guillen did get fooled twice in the 1986 season.