Infield Fly? Easy!
If any rule will cause problems, it's the Infield Fly Rule. There are so many wrong interpretations, misunderstandings, etc. with this rule. In the first place, the only place to check the definition of the rule is in the Little League Rule book. Chat rooms, Wikipedia, etc. can all be crazy with their interpretations. OK, here we go......
If there are runners on first and second, or first, second and third with less than two out, there is an infield fly possibility.
If the batter then hits a fair fly ball (not a line drive or bunt) that COULD be caught by a defensive player stationed in the infield with ORDINARY EFFORT, an Infield Fly should be called. Keep in mind, “ordinary effort” can be very different between a 9-year-old and an 18-year-old. One way to think of it is, “Is the fielder comfortable under the ball?” If so, you’ve got ordinary effort. (Jim Evans gets the credit for that one!)
The umpire must watch the ball and the fielders, and decide if the batted ball qualifies as an infield fly. If so, when the ball reaches the apex of its flight, in other words, its highest point, the umpire should point at the ball, and holler, "Infield fly, the batter's out!" If the ball is close to the foul line, say "Infield fly, if fair!" (Either/any umpire can call it.) The umpires have to watch the ball, watch the reaction of the fielders, back and forth until the ball is at the apex, then make a decision.
As soon as the umpire says “Infield fly”, the batter is out AND THE FORCE IS REMOVED FROM THE RUNNERS. Of course, that's the purpose of the rule, to keep the defense from getting a cheap double play. THE RUNNERS DO NOT HAVE TO RUN if the umpire says "Infield fly, the batter's out!"
Now, the call of "Infield fly" only affects the batter-runner....the batter-runner is immediately out which removes the force, REGARDLESS of whether the ball is caught or not. The other runners are subject to the rules regarding tagging up just as if the ball had been hit into the outfield. If it's caught, they must tag up before they advance. But if it's not caught, they do not have to tag.
Don't think of the "Infield fly" call as a "catch" because it's not. The ball has just been ruled an Infield Fly which makes the batter-runner out instantly, but the ball may or may not be caught. Whether it’s caught or not does NOT affect the Infield Fly call. Check Rule 2.00, Catch definition. This applies to an infield fly situation, too.
Also remember a few other things:
The ball stays alive during an Infield Fly play. It's not dead, so runners off base may be tagged, etc.
An infield fly is a fair fly ball which CAN be caught by an infielder with ordinary effort. That doesn't mean it HAS to be caught by an infielder. Imagine a shortstop playing deep, backing up into the outfield grass to catch a fly with, in the ump's judgment, ordinary effort. The umpire points up and calls "Infield fly, the batter is out!" But the left fielder charges in, and calls him off and catches the ball.......or doesn't catch it, either way. That is STILL an infield fly, by definition.
If the umpire calls "Infield fly, the batter's out!", or "Infield fly, if fair!" and the ball drops untouched and rolls foul; it is NOT an infield fly....just a foul ball. If it lands untouched foul, and rolls fair, it's an infield fly.
Last but not least, don't get confused with Rule 6.05k, the intentional drop. If you read that rule, you will see the differences between it and an infield fly. The infield fly rule always takes precedence. (Besides, you'll almost never see these kids intentionally drop a fly ball, they have a hard enough time catching them!!)