Search the internet for information about ‘popups baseball,’ and the first few pages of results are largely videos and tutorials aimed at young hitters — chop the ball as if you’re using an axe, keep your back elbow up, stiffen that front leg. Around the third page, you start getting some fielding tips — stay under the ball, block the sun, call off your teammates. Somewhere after the 12th page, you start getting nonsensical or irrelevant results — Tecmo Bowl and RBI baseball ROM emulator downloads, urban dictionary entries, and popup ad blockers.

Not once on the first 20 pages of results is there a ‘how to’ link for pitchers. Surely, if hitters have to avoid hitting the things, there must be a way for pitchers to induce them?

Not if inducing popups is not a repeatable skill.

User jessef at Bluebird Banter decided to see if he could pinpoint some aspect of popups as a ‘skill.’ Doing so would require showing that pitchers could repeat that skill from season to season. A successful season-to-season correlation would have major implications for our ERA estimators, which, for the most part, ignore pop-ups. Even SIERA, which uses batted ball mix, uses outfield fly balls and ground balls, and only sort of gives a nod in the direction of popups by working around it.

Soooo… long story short, he couldn’t find anything. Well, he found that 2010 popup rates did explain about 20% of the variance in 2011 popup rates — but we know that popup rates are related to ground-ball and flyball rates, and that relationship might be responsible for that 20%. And when jessef tried to control for the relationship between popups and fly balls — by finding pitchers that had more popups than they “should have had” in 2010 and then seeing if they were able to repeat that skill — he didn’t find anything. Or to say it more precisely, he found nothing.

I found that, in general, a pitcher outperforming his predicted popup rate in 2010 did not have a significant effect on him outperforming his predicted popup rate in 2011 (Rsq = 0.00, p = 0.44, 55 pitchers in sample). In other words, pitcher popup rates seem to be more constrained by overall GB/FB splits than by any specific popup-inducing tendencies.

This mirrors the work done by David Appelman two years ago, in which he found it hard to pinpoint that same skill. You may see a batter’s BABIP weighed down by popups, or a pitcher’s ERA propped up by infield flies, but you’re not likely to see that same batter or pitcher outperform or underperform his expected popup rate again the next year. Look at the league’s IFFB% going back to 2002, and you can see that although it’s down to about 10% from a high near 12%, that’s tied to an increase in ground-ball percentage (which is probably tied to an increase in league-wide velocity, which might be tied to the game’s emphasis on youth, but that’s another story).  Hit more fly balls, and you hit more infield fly balls, at least if the sample is large enough.

You might be familiar with the names that are embroiled in this ongoing discussion. Matt Cain has outperformed his career 4.19 xFIP by almost a full run. Jered Weaver calls samesies. Some have pointed to their infield fly rate as the source of that discrepancy. When faced with these players, it seems ludicrous to assume that what they are doing is not a repeatable skill. They’ve been doing it, haven’t they?

Well, with those particular players, it doesn’t seem clear that it IS their IFFB% that’s the driver. Matt Cain’s career rate is 12.5%, which is above league average (10.1% over the course of his career). But Matt Cain has given up 231 infield fly balls over his career. Had he given up 187 popups instead (the 10.1% rate), would his career ERA be a run higher? That’s 44 more outfield fly balls, and even if we use the 10% home-run-per-fly-ball number, that’s four more home runs. Five if we’re generous. Over the course of an eight-year career. You could do the same math with Jered Weaver and his 13.3% IFFB rate — and then also notice that his popup percentage this year is 10.7%, or probably within the error bar for league average. What we do know is that both of these pitchers are fly ball pitchers (so they’re due for more infield flies as well), they both have low HR/FB rates, and they both pitch in parks that suppress home runs. Perhaps that last fact has a little more to do with things their infield fly balls.

The fact remains that nobody has been able to demonstrate a league-wide skill to induce popups. If Weaver and Cain have that ability, they’d be outliers. And we have a big book on these two by now — it’s more important to be skeptical of younger pitchers with high infield fly ball rates. Jeremy Hellickson, for example, beat his estimators by a run and a half last season and is doing it again this season. Last year, a 16.2% IFFB rate helped, along with a tiny batting average on balls in play. This year, his infield fly percentage is 10.7%, or about normal for a non-ground-ball pitcher. Phil Hughes is having one of his better years. But despite many of his peripherals being in line with his production, many of his ERA estimators are skeptical. That might be because he has the second-highest popup rate this season among qualified pitchers, which, at 15.9%, is a couple ticks higher than his career rate (13.1%). Again, he’s a fly ball pitcher, so the career rate is maybe believable, but this year’s number is excessive.

It’s really as simple as this. Look at last year’s popup leaderboard, and then compare it to this year’s version. If any of the names are similar, you’ll notice they are a fly ball pitcher. And if a pitcher allows batters to put the ball in the air, they have a best case scenario (the popup) and a worst case scenario (the home run), and there’s little evidence they can do much to suppress either without a little help from their home park. As far as we can tell, inducing the popup is not a pitcher skill.

And that’s probably why there are no video tutorials telling pitchers how to induce popups.