The infield fly rule applies only when there are fewer than two outs, and there is a force play at third (runners on first and second base, or bases loaded). In these situations, if a fair fly ball is hit that, in the umpire's judgment, is catchable by an infielder with ordinary effort, the batter is out regardless of whether the ball is actually caught in flight. The rule states that the umpire is supposed to announce, "Infield fly, if fair." If the ball will be almost certainly fair, the umpire will likely yell, "Infield fly, batter's out!" or just "Batter's out!" Umpires also typically raise one arm straight up to signal to everyone that the rule is in effect.

Any fair fly ball that could have been caught by an infielder with ordinary effort is covered by the rule regardless of where the ball is caught. The ball need not be caught by an infielder, nor must it be caught in the infield. For example, if an infielder retreats to the outfield in an effort to catch a fly ball with ordinary effort, the Infield Fly Rule would be invoked, even if an outfielder ultimately caught the ball, and even if no infielder attempted to make a play on the ball. Similarly, a fly ball within the infield that could have been caught by an infielder with ordinary effort, but is caught by an outfielder, would also be covered by the rule.

On a caught infield fly, a runner must tag up (i.e., retouch, at or after the time the fly ball is first touched by a fielder, the base the runner held at the time of pitch) in order to be eligible to advance, as on any catch. If the infield fly falls to fair ground untouched, or is touched and dropped, runners need not tag up. In either case, since the batter is out, the force play on other runners is removed.

Infield Fly Rule - first baseman caught the infield fly

To score an inside-the-park home run the player must run, round, and touch all four bases before a fielder tags him out, the same as he would do for a double or triple. The play often occurs due to a fielding mishap by the defense or a strange bounce in the outfield. If the fielder commits an error during the act, however, the play is not scored as a home run, but rather advancing on an error. 

Mark "IP" next to the Home Run box to show that it was hit in the park

Triple with an overthrow error by the catcher to the thirdbaseman to go home - not marked as a home run

A FORCE PLAY is a play in which a runner legally loses his right to occupy a base by reason of the batter becoming a runner. 

A DOUBLE PLAY is a play by the defense in which two offensive players are put out as a result of continuous action, providing there is no error between putouts.

(a) A force double play is one in which both putouts are force plays.

(b) A reverse force double play is one in which the first out is a force play and the second out is made on a runner for whom the force is removed by reason of the first out.

Examples of reverse force plays: runner on first, one out; batter grounds to first baseman, who steps on first base (one out) and throws to second baseman or shortstop for the second out (a tag play).
Another example: bases loaded, none out; batter grounds to third baseman, who steps on third base (one out); then throws to catcher for the second out (tag play).

Force Double Play
Runner from second base is tagged by the third baseman (5U) who scooped up the grounder, then the ball is thrown to the second baseman (5-4) for the force out at second. 

Reverse Force Double Play
First baseman caught the fly ball (F3) then threw the ball to the shortstop (3-6) who stepped on second base before the runner could get back to retouch.

The official rulebook of Major League Baseball states:

(a) The official scorer shall credit the batter with a run batted in for every run that scores

(1) unaided by an error and as part of a play begun by the batter's safe hit (including the batter's home run), sacrifice bunt, sacrifice fly, infield out or fielder's choice, unless Rule 10.04(b) (below) applies;

(2) by reason of the batter becoming a runner with the bases full (because of a base on balls, an award of first base for being touched by a pitched ball or for interference or obstruction); or

(3) when, before two are out, an error is made on a play on which a runner from third base ordinarily would score.

(b) The official scorer shall not credit a run batted in

(1) when the batter grounds into a force double play or a reverse-force double play; or

(2) when a fielder is charged with an error because the fielder muffs a throw at first base that would have completed a force double play.

(c) The official scorer's judgment must determine whether a run batted in shall be credited for a run that scores when a fielder holds the ball or throws to a wrong base. Ordinarily, if the runner keeps going, the official scorer should credit a run batted in; if the runner stops and takes off again when the runner notices the misplay, the official scorer should credit the run as scored on a fielder's choice.

Two ways to mark an RBI on the Scoresheet:

Write "2RBI" in the top of the block

Put a dot for each RBI in the top right corner of the block

Jesse grabs a bunt as Matthew runs to first

• He is declared out before reaching first base, or
• He reaches first base safely, or
• He hits a fair ball which causes a third out on another runner (see left on base)

An at bat (AB) is used to calculate certain statistics, including batting average, on-base percentage, and slugging percentage. It is a more restricted definition of a plate appearance.  A batter has an at bat every time he faces a pitcher, except in the following circumstances:

• He receives a base on balls (BB).
• He is hit by a pitch (HBP).
• He hits a sacrifice fly or a sacrifice hit (also known as sacrifice bunt).
• He is awarded first base due to interference or obstruction, usually by the catcher.
• The inning ends while he is still at bat (due to the third out being made by a runner caught stealing, for example). In this case, the batter will come to bat again in the next inning, though he now has no balls or strikes on him.

A catcher is charged with a passed ball (PB) when he fails to hold or control a legally pitched ball that, with ordinary effort, should have been controlled, and as a result permits a runner or runners to advance. A runner who advances due to a passed ball is not credited with a stolen base unless he breaks for the base before the pitcher begins his delivery.  A passed ball is not recorded as an error but with a PB.

A closely related statistic is the wild pitch (WP).  As with many baseball statistics, whether a pitch that gets away from a catcher is a passed ball or wild pitch is at the discretion of the official scorer. Typically, pitches that are deemed to be ordinarily caught by the catcher, but are not, are ruled passed balls, while pitches that get by the catcher that are thought to have required extraordinary effort by the catcher in order to stop them are wild pitches. If the pitch was so low as to touch the ground, or so high that the catcher has to jump to get to it, or so wide that the catcher has to lunge for it, it is usually then considered a wild pitch and not a passed ball.

Since Little League does not allow lead-offs, stealing a base is extremely difficult except for the fastest of runners.  If the runner is able to take the base but is safe due to an error in the throw from the catcher or an error in the fielder catching or fielding the ball, then it is scored as an error on the appropriate defensive player and not a stolen base.

Three runners advance a base on an error by the right fielder, most likely from dropping the catch.