Backing Up the Play
Almost every time an outfielder makes a play, another outfielder is backing up the play by moving behind him. If the ball gets by the initial fielder, the other fielder is there to keep the ball from rolling all the way to the wall and allowing the runners to take extra bases.
Infielders also back up plays when they have time to react, and the catcher often backs up plays at first base, protecting against errant throws by an infielder.
Calling Off Other Players
When the ball is hit in the air, the fielder who expects to make the catch communicates this by calling off other players. On pop-ups or fly balls, the player with the best chance to catch the ball calls out “mine” or “I have it,” and everyone else backs off.
In the outfield, the center fielder is generally the best fielder and is in charge of defensive play. Thus, if he has a good chance to catch the ball, he will call off the other fielders and make the catch himself. If you see fielders collide on a fly ball, it is probably because someone did not make a call, or the fielders did not hear each other.
Hitting the Cutoff Man
When the ball is hit deep into the outfield, either for an out or a base hit, and a runner tries to advance, the player who fields the ball may opt for hitting the cutoff man. The cutoff man is an infielder who stations himself between the outfielder and the base the throw is going to.
The cutoff man’s job is to catch the long throw from the outfielder and make a shorter throw to a base. The cutoff man also catches any throws that are off target and relays them to a base. If necessary, he can cut the ball off to keep the runners from taking an extra base on a long throw.
Guarding the Lines
Fielders who are guarding the lines have moved closer to the foul lines in the infield, the outfield, or both. The purpose is to make it less likely that a batter will hit the ball fair down the line.
Fielders usually start to guard the lines when the score is close in about the seventh inning, because a ball hit down the line often results in a damaging extra-base hit. The disadvantage of guarding the lines is that it opens up the middle of the field, making it easier for the batter to hit a single to that part of the field.
The manager brings the infield in by having them station themselves closer to home plate than they normally would. They do this when a runner is on third, and they want to prevent him from scoring on a ground ball. Because they are closer to the batter, however, the infielders have less time to react when the ball is hit.
This means that the batter has a better chance of knocking the ball through the infield. Like many strategic maneuvers in baseball, bringing the infield in is a calculated risk, with the fielders gambling that the ball will be hit to them and the run will be prevented.
Infield at Double Play Depth
When the infield is at double play depth, the first and third basemen stay in their normal location, but the shortstop and second basemen move closer to second base and a couple of steps closer to home plate.
If a ground ball is hit within their range, this positioning makes it easier for them to turn a double play and make two outs.