Fly Out and Pop Up
A ball caught in the air, and the difference between a fly ball and a pop up is most of a hitter's season.
What it actually is. Any batted ball caught in the air before it lands is an out, in fair or foul territory, and runners may advance afterwards only by tagging up. A fly ball is hit into the outfield; a pop up is hit very high and very steep and usually stays in the infield. Both are outs, and they mean opposite things about the swing that produced them.
What somebody who knows the game gets out of it. The infield pop up is the worst outcome in baseball for a hitter, worse than a strikeout: it is an automatic out that also cannot advance anybody, and its rate is one of the more stable indicators that a hitter is getting beaten underneath the ball. A fly ball to the outfield, by contrast, is where every extra base hit comes from. This is why launch angle alone is not the goal and why the barrel definition pairs angle with exit velocity: the same uppercut that produces a 28 degree line drive at 100 mph produces a 55 degree pop up at 80.
The numbers worth knowing. Around 35 percent of balls in play are fly balls and about 7 to 8 percent are infield pop ups. A pop up is converted into an out over 98 percent of the time, which is a higher out rate than a strikeout since a strikeout can be uncaught.
What people get wrong about it. A can of corn is not a scoring term, it is just a lazy fly ball. The infield fly rule is a different thing entirely: with runners on first and second, or bases loaded, and fewer than two out, a catchable infield pop up is an automatic out whether or not it is caught, so the defense cannot let it drop and turn two.
At Little League and travel ball. Fly balls are the hardest defensive play at youth level by a distance, so the same batted ball that is an automatic out in the majors is a two base error at 9U. That is exactly why teaching youth hitters to hit the ball in the air produces short term results and long term problems, and why fly ball reads are one of the drills the struggles section covers.
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