When should I call an infield fly?

Call it when all of these apply:

1. fewer than two outs,
2. runners on first and second, or first, second and third,
3. a fair fly ball that is not a line drive or a bunt, and
4. an infielder can catch it with ordinary effort. The pitcher, catcher and any outfielder positioned in the infield count as infielders.

The batter is out, but the ball stays live. Runners may advance at their own risk; if the ball is caught they must retouch, and if it drops they aren't forced. If it becomes foul, it's a foul ball.

A runner touching their base who is hit by the ball on an infield fly is not out. The rule protects runners, so when in doubt and an easy double play is possible, call it.